source: libcfa/src/concurrency/io.cfa @ 31bb2e1

//
// Cforall Version 1.0.0 Copyright (C) 2020 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// io.cfa --
//
// Author           : Thierry Delisle
// Created On       : Thu Apr 23 17:31:00 2020
// Last Modified By :
// Last Modified On :
// Update Count     :
//

// #define __CFA_DEBUG_PRINT_IO__
// #define __CFA_DEBUG_PRINT_IO_CORE__

#include "kernel.hfa"
#include "bitmanip.hfa"

#if !defined(HAVE_LINUX_IO_URING_H)
        void __kernel_io_startup( cluster &, unsigned, bool ) {
                // Nothing to do without io_uring
        }

        void __kernel_io_finish_start( cluster & ) {
                // Nothing to do without io_uring
        }

        void __kernel_io_prepare_stop( cluster & ) {
                // Nothing to do without io_uring
        }

        void __kernel_io_shutdown( cluster &, bool ) {
                // Nothing to do without io_uring
        }

#else
        #define _GNU_SOURCE         /* See feature_test_macros(7) */
        #include <errno.h>
        #include <stdint.h>
        #include <string.h>
        #include <unistd.h>
        #include <sys/mman.h>

        extern "C" {
                #include <sys/syscall.h>

                #include <linux/io_uring.h>
        }

        #include "bits/signal.hfa"
        #include "kernel_private.hfa"
        #include "thread.hfa"

        uint32_t entries_per_cluster() {
                return 256;
        }

        static void * __io_poller_slow( void * arg );

        // Weirdly, some systems that do support io_uring don't actually define these
        #ifdef __alpha__
                /*
                * alpha is the only exception, all other architectures
                * have common numbers for new system calls.
                */
                #ifndef __NR_io_uring_setup
                        #define __NR_io_uring_setup           535
                #endif
                #ifndef __NR_io_uring_enter
                        #define __NR_io_uring_enter           536
                #endif
                #ifndef __NR_io_uring_register
                        #define __NR_io_uring_register        537
                #endif
        #else /* !__alpha__ */
                #ifndef __NR_io_uring_setup
                        #define __NR_io_uring_setup           425
                #endif
                #ifndef __NR_io_uring_enter
                        #define __NR_io_uring_enter           426
                #endif
                #ifndef __NR_io_uring_register
                        #define __NR_io_uring_register        427
                #endif
        #endif

        // Fast poller user-thread
        // Not using the "thread" keyword because we want to control
        // more carefully when to start/stop it
        struct __io_poller_fast {
                struct __io_data * ring;
                $thread thrd;
        };

        void ?{}( __io_poller_fast & this, struct cluster & cltr ) {
                this.ring = cltr.io;
                (this.thrd){ "Fast I/O Poller", cltr };
        }
        void ^?{}( __io_poller_fast & mutex this );
        void main( __io_poller_fast & this );
        static inline $thread * get_thread( __io_poller_fast & this ) { return &this.thrd; }
        void ^?{}( __io_poller_fast & mutex this ) {}

        struct __submition_data {
                // Head and tail of the ring (associated with array)
                volatile uint32_t * head;
                volatile uint32_t * tail;

                // The actual kernel ring which uses head/tail
                // indexes into the sqes arrays
                uint32_t * array;

                // number of entries and mask to go with it
                const uint32_t * num;
                const uint32_t * mask;

                // Submission flags (Not sure what for)
                uint32_t * flags;

                // number of sqes not submitted (whatever that means)
                uint32_t * dropped;

                // Like head/tail but not seen by the kernel
                volatile uint32_t * ready;
                uint32_t ready_cnt;

                __spinlock_t lock;

                // A buffer of sqes (not the actual ring)
                struct io_uring_sqe * sqes;

                // The location and size of the mmaped area
                void * ring_ptr;
                size_t ring_sz;
        };

        struct __completion_data {
                // Head and tail of the ring
                volatile uint32_t * head;
                volatile uint32_t * tail;

                // number of entries and mask to go with it
                const uint32_t * mask;
                const uint32_t * num;

                // number of cqes not submitted (whatever that means)
                uint32_t * overflow;

                // the kernel ring
                struct io_uring_cqe * cqes;

                // The location and size of the mmaped area
                void * ring_ptr;
                size_t ring_sz;
        };

        struct __io_data {
                struct __submition_data submit_q;
                struct __completion_data completion_q;
                uint32_t ring_flags;
                int cltr_flags;
                int fd;
                semaphore submit;
                volatile bool done;
                struct {
                        struct {
                                __processor_id_t id;
                                void * stack;
                                pthread_t kthrd;
                                volatile bool blocked;
                        } slow;
                        __io_poller_fast fast;
                        __bin_sem_t sem;
                } poller;
        };

//=============================================================================================
// I/O Startup / Shutdown logic
//=============================================================================================
        void __kernel_io_startup( cluster & this, unsigned io_flags, bool main_cluster ) {
                this.io = malloc();

                // Step 1 : call to setup
                struct io_uring_params params;
                memset(&params, 0, sizeof(params));

                uint32_t nentries = entries_per_cluster();

                int fd = syscall(__NR_io_uring_setup, nentries, &params );
                if(fd < 0) {
                        abort("KERNEL ERROR: IO_URING SETUP - %s\n", strerror(errno));
                }

                // Step 2 : mmap result
                memset( this.io, 0, sizeof(struct __io_data) );
                struct __submition_data  & sq = this.io->submit_q;
                struct __completion_data & cq = this.io->completion_q;

                // calculate the right ring size
                sq.ring_sz = params.sq_off.array + (params.sq_entries * sizeof(unsigned)           );
                cq.ring_sz = params.cq_off.cqes  + (params.cq_entries * sizeof(struct io_uring_cqe));

                // Requires features
                #if defined(IORING_FEAT_SINGLE_MMAP)
                        // adjust the size according to the parameters
                        if ((params.features & IORING_FEAT_SINGLE_MMAP) != 0) {
                                cq->ring_sz = sq->ring_sz = max(cq->ring_sz, sq->ring_sz);
                        }
                #endif

                // mmap the Submit Queue into existence
                sq.ring_ptr = mmap(0, sq.ring_sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd, IORING_OFF_SQ_RING);
                if (sq.ring_ptr == (void*)MAP_FAILED) {
                        abort("KERNEL ERROR: IO_URING MMAP1 - %s\n", strerror(errno));
                }

                // Requires features
                #if defined(IORING_FEAT_SINGLE_MMAP)
                        // mmap the Completion Queue into existence (may or may not be needed)
                        if ((params.features & IORING_FEAT_SINGLE_MMAP) != 0) {
                                cq->ring_ptr = sq->ring_ptr;
                        }
                        else
                #endif
                {
                        // We need multiple call to MMAP
                        cq.ring_ptr = mmap(0, cq.ring_sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd, IORING_OFF_CQ_RING);
                        if (cq.ring_ptr == (void*)MAP_FAILED) {
                                munmap(sq.ring_ptr, sq.ring_sz);
                                abort("KERNEL ERROR: IO_URING MMAP2 - %s\n", strerror(errno));
                        }
                }

                // mmap the submit queue entries
                size_t size = params.sq_entries * sizeof(struct io_uring_sqe);
                sq.sqes = (struct io_uring_sqe *)mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd, IORING_OFF_SQES);
                if (sq.sqes == (struct io_uring_sqe *)MAP_FAILED) {
                        munmap(sq.ring_ptr, sq.ring_sz);
                        if (cq.ring_ptr != sq.ring_ptr) munmap(cq.ring_ptr, cq.ring_sz);
                        abort("KERNEL ERROR: IO_URING MMAP3 - %s\n", strerror(errno));
                }

                // Get the pointers from the kernel to fill the structure
                // submit queue
                sq.head    = (volatile uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.head);
                sq.tail    = (volatile uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.tail);
                sq.mask    = (   const uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.ring_mask);
                sq.num     = (   const uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.ring_entries);
                sq.flags   = (         uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.flags);
                sq.dropped = (         uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.dropped);
                sq.array   = (         uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.array);

                {
                        const uint32_t num = *sq.num;
                        for( i; num ) {
                                sq.sqes[i].user_data = 0ul64;
                        }
                }

                if( io_flags & CFA_CLUSTER_IO_POLLER_THREAD_SUBMITS ) {
                        /* paranoid */ verify( is_pow2( io_flags >> CFA_CLUSTER_IO_BUFFLEN_OFFSET ) || ((io_flags >> CFA_CLUSTER_IO_BUFFLEN_OFFSET) < 8)  );
                        sq.ready_cnt = max(io_flags >> CFA_CLUSTER_IO_BUFFLEN_OFFSET, 8);
                        sq.ready = alloc_align( 64, sq.ready_cnt );
                        for(i; sq.ready_cnt) {
                                sq.ready[i] = -1ul32;
                        }
                }
                else {
                        sq.ready_cnt = 0;
                        sq.ready = 0p;
                }

                // completion queue
                cq.head     = (volatile uint32_t *)(((intptr_t)cq.ring_ptr) + params.cq_off.head);
                cq.tail     = (volatile uint32_t *)(((intptr_t)cq.ring_ptr) + params.cq_off.tail);
                cq.mask     = (   const uint32_t *)(((intptr_t)cq.ring_ptr) + params.cq_off.ring_mask);
                cq.num      = (   const uint32_t *)(((intptr_t)cq.ring_ptr) + params.cq_off.ring_entries);
                cq.overflow = (         uint32_t *)(((intptr_t)cq.ring_ptr) + params.cq_off.overflow);
                cq.cqes   = (struct io_uring_cqe *)(((intptr_t)cq.ring_ptr) + params.cq_off.cqes);

                // some paranoid checks
                /* paranoid */ verifyf( (*cq.mask) == ((*cq.num) - 1ul32), "IO_URING Expected mask to be %u (%u entries), was %u", (*cq.num) - 1ul32, *cq.num, *cq.mask  );
                /* paranoid */ verifyf( (*cq.num)  >= nentries, "IO_URING Expected %u entries, got %u", nentries, *cq.num );
                /* paranoid */ verifyf( (*cq.head) == 0, "IO_URING Expected head to be 0, got %u", *cq.head );
                /* paranoid */ verifyf( (*cq.tail) == 0, "IO_URING Expected tail to be 0, got %u", *cq.tail );

                /* paranoid */ verifyf( (*sq.mask) == ((*sq.num) - 1ul32), "IO_URING Expected mask to be %u (%u entries), was %u", (*sq.num) - 1ul32, *sq.num, *sq.mask );
                /* paranoid */ verifyf( (*sq.num) >= nentries, "IO_URING Expected %u entries, got %u", nentries, *sq.num );
                /* paranoid */ verifyf( (*sq.head) == 0, "IO_URING Expected head to be 0, got %u", *sq.head );
                /* paranoid */ verifyf( (*sq.tail) == 0, "IO_URING Expected tail to be 0, got %u", *sq.tail );

                // Update the global ring info
                this.io->ring_flags = params.flags;
                this.io->cltr_flags = io_flags;
                this.io->fd         = fd;
                this.io->done       = false;
                (this.io->submit){ min(*sq.num, *cq.num) };

                if(!main_cluster) {
                        __kernel_io_finish_start( this );
                }
        }

        void __kernel_io_finish_start( cluster & this ) {
                if( this.io->cltr_flags & CFA_CLUSTER_IO_POLLER_USER_THREAD ) {
                        __cfadbg_print_safe(io_core, "Kernel I/O : Creating fast poller for cluter %p\n", &this);
                        (this.io->poller.fast){ this };
                        __thrd_start( this.io->poller.fast, main );
                }

                // Create the poller thread
                __cfadbg_print_safe(io_core, "Kernel I/O : Creating slow poller for cluter %p\n", &this);
                this.io->poller.slow.blocked = false;
                this.io->poller.slow.stack = __create_pthread( &this.io->poller.slow.kthrd, __io_poller_slow, &this );
        }

        void __kernel_io_prepare_stop( cluster & this ) {
                __cfadbg_print_safe(io_core, "Kernel I/O : Stopping pollers for cluster\n", &this);
                // Notify the poller thread of the shutdown
                __atomic_store_n(&this.io->done, true, __ATOMIC_SEQ_CST);

                // Stop the IO Poller
                sigval val = { 1 };
                pthread_sigqueue( this.io->poller.slow.kthrd, SIGUSR1, val );
                post( this.io->poller.sem );

                // Wait for the poller thread to finish
                pthread_join( this.io->poller.slow.kthrd, 0p );
                free( this.io->poller.slow.stack );

                __cfadbg_print_safe(io_core, "Kernel I/O : Slow poller stopped for cluster\n", &this);

                if( this.io->cltr_flags & CFA_CLUSTER_IO_POLLER_USER_THREAD ) {
                        with( this.io->poller.fast ) {
                                /* paranoid */ verify( this.nprocessors == 0 || &this == mainCluster );
                                /* paranoid */ verify( !ready_mutate_islocked() );

                                // We need to adjust the clean-up based on where the thread is
                                if( thrd.state == Ready || thrd.preempted != __NO_PREEMPTION ) {

                                        ready_schedule_lock( (struct __processor_id_t *)active_processor() );

                                                // This is the tricky case
                                                // The thread was preempted and now it is on the ready queue
                                                // The thread should be the last on the list
                                                /* paranoid */ verify( thrd.link.next != 0p );

                                                // Remove the thread from the ready queue of this cluster
                                                __attribute__((unused)) bool removed = remove_head( &this, &thrd );
                                                /* paranoid */ verify( removed );
                                                thrd.link.next = 0p;
                                                thrd.link.prev = 0p;
                                                __cfaabi_dbg_debug_do( thrd.unpark_stale = true );

                                                // Fixup the thread state
                                                thrd.state = Blocked;
                                                thrd.ticket = 0;
                                                thrd.preempted = __NO_PREEMPTION;

                                        ready_schedule_unlock( (struct __processor_id_t *)active_processor() );

                                        // Pretend like the thread was blocked all along
                                }
                                // !!! This is not an else if !!!
                                if( thrd.state == Blocked ) {

                                        // This is the "easy case"
                                        // The thread is parked and can easily be moved to active cluster
                                        verify( thrd.curr_cluster != active_cluster() || thrd.curr_cluster == mainCluster );
                                        thrd.curr_cluster = active_cluster();

                                        // unpark the fast io_poller
                                        unpark( &thrd __cfaabi_dbg_ctx2 );
                                }
                                else {

                                        // The thread is in a weird state
                                        // I don't know what to do here
                                        abort("Fast poller thread is in unexpected state, cannot clean-up correctly\n");
                                }

                        }

                        ^(this.io->poller.fast){};

                        __cfadbg_print_safe(io_core, "Kernel I/O : Fast poller stopped for cluster\n", &this);
                }
        }

        void __kernel_io_shutdown( cluster & this, bool main_cluster ) {
                if(!main_cluster) {
                        __kernel_io_prepare_stop( this );
                }

                // Shutdown the io rings
                struct __submition_data  & sq = this.io->submit_q;
                struct __completion_data & cq = this.io->completion_q;

                // unmap the submit queue entries
                munmap(sq.sqes, (*sq.num) * sizeof(struct io_uring_sqe));

                // unmap the Submit Queue ring
                munmap(sq.ring_ptr, sq.ring_sz);

                // unmap the Completion Queue ring, if it is different
                if (cq.ring_ptr != sq.ring_ptr) {
                        munmap(cq.ring_ptr, cq.ring_sz);
                }

                // close the file descriptor
                close(this.io->fd);

                free( this.io->submit_q.ready ); // Maybe null, doesn't matter
                free( this.io );
        }

//=============================================================================================
// I/O Polling
//=============================================================================================
        // Process a single completion message from the io_uring
        // This is NOT thread-safe
        static [int, bool] __drain_io( & struct __io_data ring, * sigset_t mask, int waitcnt, bool in_kernel ) {
                unsigned to_submit = 0;
                if( ring.cltr_flags & CFA_CLUSTER_IO_POLLER_THREAD_SUBMITS ) {

                        // If the poller thread also submits, then we need to aggregate the submissions which are ready
                        uint32_t tail = *ring.submit_q.tail;
                        const uint32_t mask = *ring.submit_q.mask;

                        // Go through the list of ready submissions
                        for( i; ring.submit_q.ready_cnt ) {
                                // replace any submission with the sentinel, to consume it.
                                uint32_t idx = __atomic_exchange_n( &ring.submit_q.ready[i], -1ul32, __ATOMIC_RELAXED);

                                // If it was already the sentinel, then we are done
                                if( idx == -1ul32 ) continue;

                                // If we got a real submission, append it to the list
                                ring.submit_q.array[ (tail + to_submit) & mask ] = idx & mask;
                                to_submit++;
                        }

                        // Increment the tail based on how many we are ready to submit
                        __atomic_fetch_add(ring.submit_q.tail, to_submit, __ATOMIC_SEQ_CST);
                }

                const uint32_t smask = *ring.submit_q.mask;
                uint32_t shead = *ring.submit_q.head;
                int ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, waitcnt, IORING_ENTER_GETEVENTS, mask, _NSIG / 8);
                if( ret < 0 ) {
                        switch((int)errno) {
                        case EAGAIN:
                        case EINTR:
                                return -EAGAIN;
                        default:
                                abort( "KERNEL ERROR: IO_URING WAIT - %s\n", strerror(errno) );
                        }
                }

                // Release the consumed SQEs
                for( i; ret ) {
                        uint32_t idx = ring.submit_q.array[ (i + shead) & smask ];
                        ring.submit_q.sqes[ idx ].user_data = 0;
                }

                uint32_t avail = 0;
                uint32_t sqe_num = *ring.submit_q.num;
                for(i; sqe_num) {
                        if( ring.submit_q.sqes[ i ].user_data == 0 ) avail++;
                }

                // update statistics
                #if !defined(__CFA_NO_STATISTICS__)
                        __tls_stats()->io.submit_q.submit_avg.rdy += to_submit;
                        __tls_stats()->io.submit_q.submit_avg.csm += ret;
                        __tls_stats()->io.submit_q.submit_avg.avl += avail;
                        __tls_stats()->io.submit_q.submit_avg.cnt += 1;
                #endif

                // Drain the queue
                unsigned head = *ring.completion_q.head;
                unsigned tail = *ring.completion_q.tail;
                const uint32_t mask = *ring.completion_q.mask;

                // Memory barrier
                __atomic_thread_fence( __ATOMIC_SEQ_CST );

                // Nothing was new return 0
                if (head == tail) {
                        return 0;
                }

                uint32_t count = tail - head;
                for(i; count) {
                        unsigned idx = (head + i) & mask;
                        struct io_uring_cqe & cqe = ring.completion_q.cqes[idx];

                        /* paranoid */ verify(&cqe);

                        struct __io_user_data_t * data = (struct __io_user_data_t *)(uintptr_t)cqe.user_data;
                        __cfadbg_print_safe( io, "Kernel I/O : Performed reading io cqe %p, result %d for %p\n", data, cqe.res, data->thrd );

                        data->result = cqe.res;
                        if(!in_kernel) { unpark( data->thrd __cfaabi_dbg_ctx2 ); }
                        else         { __unpark( &ring.poller.slow.id, data->thrd __cfaabi_dbg_ctx2 ); }
                }

                // Allow new submissions to happen
                // V(ring.submit, count);

                // Mark to the kernel that the cqe has been seen
                // Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
                __atomic_thread_fence( __ATOMIC_SEQ_CST );
                __atomic_fetch_add( ring.completion_q.head, count, __ATOMIC_RELAXED );

                return [count, count > 0 || to_submit > 0];
        }

        static void * __io_poller_slow( void * arg ) {
                #if !defined( __CFA_NO_STATISTICS__ )
                        __stats_t local_stats;
                        __init_stats( &local_stats );
                        kernelTLS.this_stats = &local_stats;
                #endif

                cluster * cltr = (cluster *)arg;
                struct __io_data & ring = *cltr->io;

                ring.poller.slow.id.id = doregister( &ring.poller.slow.id );

                sigset_t mask;
                sigfillset(&mask);
                if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
                        abort( "KERNEL ERROR: IO_URING - pthread_sigmask" );
                }

                sigdelset( &mask, SIGUSR1 );

                verify( (*ring.submit_q.head) == (*ring.submit_q.tail) );
                verify( (*ring.completion_q.head) == (*ring.completion_q.tail) );

                __cfadbg_print_safe(io_core, "Kernel I/O : Slow poller for ring %p ready\n", &ring);

                if( ring.cltr_flags & CFA_CLUSTER_IO_POLLER_USER_THREAD ) {
                        while(!__atomic_load_n(&ring.done, __ATOMIC_SEQ_CST)) {

                                __atomic_store_n( &ring.poller.slow.blocked, true, __ATOMIC_SEQ_CST );

                                // In the user-thread approach drain and if anything was drained,
                                // batton pass to the user-thread
                                int count;
                                bool again;
                                [count, again] = __drain_io( ring, &mask, 1, true );

                                __atomic_store_n( &ring.poller.slow.blocked, false, __ATOMIC_SEQ_CST );

                                // Update statistics
                                #if !defined(__CFA_NO_STATISTICS__)
                                        __tls_stats()->io.complete_q.completed_avg.val += count;
                                        __tls_stats()->io.complete_q.completed_avg.slow_cnt += 1;
                                #endif

                                if(again) {
                                        __cfadbg_print_safe(io_core, "Kernel I/O : Moving to ring %p to fast poller\n", &ring);
                                        __unpark( &ring.poller.slow.id, &ring.poller.fast.thrd __cfaabi_dbg_ctx2 );
                                        wait( ring.poller.sem );
                                }
                        }
                }
                else {
                        while(!__atomic_load_n(&ring.done, __ATOMIC_SEQ_CST)) {
                                //In the naive approach, just poll the io completion queue directly
                                int count;
                                bool again;
                                [count, again] = __drain_io( ring, &mask, 1, true );

                                // Update statistics
                                #if !defined(__CFA_NO_STATISTICS__)
                                        __tls_stats()->io.complete_q.completed_avg.val += count;
                                        __tls_stats()->io.complete_q.completed_avg.slow_cnt += 1;
                                #endif
                        }
                }

                __cfadbg_print_safe(io_core, "Kernel I/O : Slow poller for ring %p stopping\n", &ring);

                unregister( &ring.poller.slow.id );

                return 0p;
        }

        void main( __io_poller_fast & this ) {
                verify( this.ring->cltr_flags & CFA_CLUSTER_IO_POLLER_USER_THREAD );

                // Start parked
                park( __cfaabi_dbg_ctx );

                __cfadbg_print_safe(io_core, "Kernel I/O : Fast poller for ring %p ready\n", &this.ring);

                int reset = 0;

                // Then loop until we need to start
                while(!__atomic_load_n(&this.ring->done, __ATOMIC_SEQ_CST)) {

                        // Drain the io
                        int count;
                        bool again;
                        disable_interrupts();
                                [count, again] = __drain_io( *this.ring, 0p, 0, false );

                                if(!again) reset++;

                                // Update statistics
                                #if !defined(__CFA_NO_STATISTICS__)
                                        __tls_stats()->io.complete_q.completed_avg.val += count;
                                        __tls_stats()->io.complete_q.completed_avg.fast_cnt += 1;
                                #endif
                        enable_interrupts( __cfaabi_dbg_ctx );

                        // If we got something, just yield and check again
                        if(reset < 5) {
                                yield();
                        }
                        // We didn't get anything baton pass to the slow poller
                        else {
                                __cfadbg_print_safe(io_core, "Kernel I/O : Moving to ring %p to slow poller\n", &this.ring);
                                reset = 0;

                                // wake up the slow poller
                                post( this.ring->poller.sem );

                                // park this thread
                                park( __cfaabi_dbg_ctx );
                        }
                }

                __cfadbg_print_safe(io_core, "Kernel I/O : Fast poller for ring %p stopping\n", &this.ring);
        }

        static inline void __wake_poller( struct __io_data & ring ) __attribute__((artificial));
        static inline void __wake_poller( struct __io_data & ring ) {
                if(!__atomic_load_n( &ring.poller.slow.blocked, __ATOMIC_SEQ_CST)) return;

                sigval val = { 1 };
                pthread_sigqueue( ring.poller.slow.kthrd, SIGUSR1, val );
        }

//=============================================================================================
// I/O Submissions
//=============================================================================================

// Submition steps :
// 1 - We need to make sure we don't overflow any of the buffer, P(ring.submit) to make sure
//     entries are available. The semaphore make sure that there is no more operations in
//     progress then the number of entries in the buffer. This probably limits concurrency
//     more than necessary since submitted but not completed operations don't need any
//     entries in user space. However, I don't know what happens if we overflow the buffers
//     because too many requests completed at once. This is a safe approach in all cases.
//     Furthermore, with hundreds of entries, this may be okay.
//
// 2 - Allocate a queue entry. The ring already has memory for all entries but only the ones
//     listed in sq.array are visible by the kernel. For those not listed, the kernel does not
//     offer any assurance that an entry is not being filled by multiple flags. Therefore, we
//     need to write an allocator that allows allocating concurrently.
//
// 3 - Actually fill the submit entry, this is the only simple and straightforward step.
//
// 4 - Append the entry index to the array and adjust the tail accordingly. This operation
//     needs to arrive to two concensus at the same time:
//     A - The order in which entries are listed in the array: no two threads must pick the
//         same index for their entries
//     B - When can the tail be update for the kernel. EVERY entries in the array between
//         head and tail must be fully filled and shouldn't ever be touched again.
//

        [* struct io_uring_sqe, uint32_t] __submit_alloc( struct __io_data & ring, uint64_t data ) {
                verify( data != 0 );


                // Prepare the data we need
                __attribute((unused)) int len   = 0;
                __attribute((unused)) int block = 0;
                uint32_t cnt = *ring.submit_q.num;
                uint32_t mask = *ring.submit_q.mask;

                disable_interrupts();
                        uint32_t off = __tls_rand();
                enable_interrupts( __cfaabi_dbg_ctx );

                // Loop around looking for an available spot
                for() {
                        // Look through the list starting at some offset
                        for(i; cnt) {
                                uint64_t expected = 0;
                                uint32_t idx = (i + off) & mask;
                                struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
                                volatile uint64_t * udata = &sqe->user_data;

                                if( *udata == expected &&
                                        __atomic_compare_exchange_n( udata, &expected, data, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) )
                                {
                                        // update statistics
                                        #if !defined(__CFA_NO_STATISTICS__)
                                                disable_interrupts();
                                                        __tls_stats()->io.submit_q.alloc_avg.val   += len;
                                                        __tls_stats()->io.submit_q.alloc_avg.block += block;
                                                        __tls_stats()->io.submit_q.alloc_avg.cnt   += 1;
                                                enable_interrupts( __cfaabi_dbg_ctx );
                                        #endif


                                        // Success return the data
                                        return [sqe, idx];
                                }
                                verify(expected != data);

                                len ++;
                        }

                        block++;
                        yield();
                }
        }

        void __submit( struct __io_data & ring, uint32_t idx ) {
                // Get now the data we definetely need
                uint32_t * const tail = ring.submit_q.tail;
                const uint32_t mask = *ring.submit_q.mask;

                disable_interrupts();

                // There are 2 submission schemes, check which one we are using
                if( ring.cltr_flags & CFA_CLUSTER_IO_POLLER_THREAD_SUBMITS ) {
                        // If the poller thread submits, then we just need to add this to the ready array

                        /* paranoid */ verify( idx <= mask   );
                        /* paranoid */ verify( idx != -1ul32 );

                        // We need to find a spot in the ready array
                        __attribute((unused)) int len   = 0;
                        __attribute((unused)) int block = 0;
                        uint32_t ready_mask = ring.submit_q.ready_cnt - 1;
                        uint32_t off = __tls_rand();
                        LOOKING: for() {
                                for(i; ring.submit_q.ready_cnt) {
                                        uint32_t ii = (i + off) & ready_mask;
                                        uint32_t expected = -1ul32;
                                        if( __atomic_compare_exchange_n( &ring.submit_q.ready[ii], &expected, idx, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) ) {
                                                break LOOKING;
                                        }
                                        verify(expected != idx);

                                        len ++;
                                }

                                block++;
                                yield();
                        }

                        __wake_poller( ring );

                        // update statistics
                        #if !defined(__CFA_NO_STATISTICS__)
                                __tls_stats()->io.submit_q.look_avg.val   += len;
                                __tls_stats()->io.submit_q.look_avg.block += block;
                                __tls_stats()->io.submit_q.look_avg.cnt   += 1;
                        #endif

                        __cfadbg_print_safe( io, "Kernel I/O : Added %u to ready for %p\n", idx, active_thread() );
                }
                else {
                        // get mutual exclusion
                        lock(ring.submit_q.lock __cfaabi_dbg_ctx2);

                        // Append to the list of ready entries

                        /* paranoid */ verify( idx <= mask );

                        ring.submit_q.array[ (*tail) & mask ] = idx & mask;
                        __atomic_fetch_add(tail, 1ul32, __ATOMIC_SEQ_CST);

                        // Submit however, many entries need to be submitted
                        int ret = syscall( __NR_io_uring_enter, ring.fd, 1, 0, 0, 0p, 0);
                        if( ret < 0 ) {
                                switch((int)errno) {
                                default:
                                        abort( "KERNEL ERROR: IO_URING SUBMIT - %s\n", strerror(errno) );
                                }
                        }

                        // update statistics
                        #if !defined(__CFA_NO_STATISTICS__)
                                __tls_stats()->io.submit_q.submit_avg.csm += 1;
                                __tls_stats()->io.submit_q.submit_avg.cnt += 1;
                        #endif

                        ring.submit_q.sqes[ idx & mask ].user_data = 0;

                        unlock(ring.submit_q.lock);

                        __cfadbg_print_safe( io, "Kernel I/O : Performed io_submit for %p, returned %d\n", active_thread(), ret );
                }

                enable_interrupts( __cfaabi_dbg_ctx );
        }

        static inline void ?{}(struct io_uring_sqe & this, uint8_t opcode, int fd) {
                this.opcode = opcode;
                #if !defined(IOSQE_ASYNC)
                        this.flags = 0;
                #else
                        this.flags = IOSQE_ASYNC;
                #endif
                this.ioprio = 0;
                this.fd = fd;
                this.off = 0;
                this.addr = 0;
                this.len = 0;
                this.rw_flags = 0;
                this.__pad2[0] = this.__pad2[1] = this.__pad2[2] = 0;
        }

        static inline void ?{}(struct io_uring_sqe & this, uint8_t opcode, int fd, void * addr, uint32_t len, uint64_t off ) {
                (this){ opcode, fd };
                this.off = off;
                this.addr = (uint64_t)(uintptr_t)addr;
                this.len = len;
        }