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io.cfa @ fd365da

ADTast-experimentalpthread-emulationqualifiedEnum

Last change on this file since fd365da was 7affcda, checked in by Thierry Delisle <tdelisle@…>, 2 years ago
Fixed a bug where io wouldn't drain everything if the completion queue is filled
Property mode set to `100644`
File size: 21.6 KB

Line
1	//
2	// Cforall Version 1.0.0 Copyright (C) 2020 University of Waterloo
3	//
4	// The contents of this file are covered under the licence agreement in the
5	// file "LICENCE" distributed with Cforall.
6	//
7	// io.cfa --
8	//
9	// Author : Thierry Delisle
10	// Created On : Thu Apr 23 17:31:00 2020
11	// Last Modified By :
12	// Last Modified On :
13	// Update Count :
14	//
15
16	#define __cforall_thread__
17	#define _GNU_SOURCE
18
19	#if defined(__CFA_DEBUG__)
20	// #define __CFA_DEBUG_PRINT_IO__
21	// #define __CFA_DEBUG_PRINT_IO_CORE__
22	#endif
23
24
25	#if defined(CFA_HAVE_LINUX_IO_URING_H)
26	#include <errno.h>
27	#include <signal.h>
28	#include <stdint.h>
29	#include <string.h>
30	#include <unistd.h>
31
32	extern "C" {
33	#include <sys/syscall.h>
34	#include <sys/eventfd.h>
35	#include <sys/uio.h>
36
37	#include <linux/io_uring.h>
38	}
39
40	#include "stats.hfa"
41	#include "kernel.hfa"
42	#include "kernel/fwd.hfa"
43	#include "kernel/private.hfa"
44	#include "kernel/cluster.hfa"
45	#include "io/types.hfa"
46
47	__attribute__((unused)) static const char * opcodes[] = {
48	"OP_NOP",
49	"OP_READV",
50	"OP_WRITEV",
51	"OP_FSYNC",
52	"OP_READ_FIXED",
53	"OP_WRITE_FIXED",
54	"OP_POLL_ADD",
55	"OP_POLL_REMOVE",
56	"OP_SYNC_FILE_RANGE",
57	"OP_SENDMSG",
58	"OP_RECVMSG",
59	"OP_TIMEOUT",
60	"OP_TIMEOUT_REMOVE",
61	"OP_ACCEPT",
62	"OP_ASYNC_CANCEL",
63	"OP_LINK_TIMEOUT",
64	"OP_CONNECT",
65	"OP_FALLOCATE",
66	"OP_OPENAT",
67	"OP_CLOSE",
68	"OP_FILES_UPDATE",
69	"OP_STATX",
70	"OP_READ",
71	"OP_WRITE",
72	"OP_FADVISE",
73	"OP_MADVISE",
74	"OP_SEND",
75	"OP_RECV",
76	"OP_OPENAT2",
77	"OP_EPOLL_CTL",
78	"OP_SPLICE",
79	"OP_PROVIDE_BUFFERS",
80	"OP_REMOVE_BUFFERS",
81	"OP_TEE",
82	"INVALID_OP"
83	};
84
85	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want );
86	static void __ioarbiter_submit( $io_context * , __u32 idxs[], __u32 have, bool lazy );
87	static void __ioarbiter_flush ( $io_context & );
88	static inline void __ioarbiter_notify( $io_context & ctx );
89	//=============================================================================================
90	// I/O Polling
91	//=============================================================================================
92	static inline unsigned __flush( struct $io_context & );
93	static inline __u32 __release_sqes( struct $io_context & );
94	extern void __kernel_unpark( thread$ * thrd, unpark_hint );
95
96	static void ioring_syscsll( struct $io_context & ctx, unsigned int min_comp, unsigned int flags ) {
97	__STATS__( true, io.calls.flush++; )
98	int ret;
99	for() {
100	ret = syscall( __NR_io_uring_enter, ctx.fd, ctx.sq.to_submit, min_comp, flags, (sigset_t *)0p, _NSIG / 8);
101	if( ret < 0 ) {
102	switch((int)errno) {
103	case EINTR:
104	continue;
105	case EAGAIN:
106	case EBUSY:
107	// Update statistics
108	__STATS__( false, io.calls.errors.busy ++; )
109	return false;
110	default:
111	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
112	}
113	}
114	break;
115	}
116
117	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring %d\n", ret, ctx.fd);
118	__STATS__( true, io.calls.submitted += ret; )
119	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
120	/* paranoid */ verify( ctx.sq.to_submit >= ret );
121
122	ctx.sq.to_submit -= ret;
123
124	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
125
126	// Release the consumed SQEs
127	__release_sqes( ctx );
128
129	/* paranoid */ verify( ! __preemption_enabled() );
130
131	__atomic_store_n(&ctx.proc->io.pending, false, __ATOMIC_RELAXED);
132	}
133
134	static bool try_acquire( $io_context * ctx ) __attribute__((nonnull(1))) {
135	/* paranoid */ verify( ! __preemption_enabled() );
136	/* paranoid */ verify( ready_schedule_islocked() );
137
138
139	{
140	const __u32 head = *ctx->cq.head;
141	const __u32 tail = *ctx->cq.tail;
142
143	if(head == tail) return false;
144	}
145
146	// Drain the queue
147	if(!__atomic_try_acquire(&ctx->cq.lock)) {
148	__STATS__( false, io.calls.locked++; )
149	return false;
150	}
151
152	return true;
153	}
154
155	static bool __cfa_do_drain( $io_context * ctx, cluster * cltr ) __attribute__((nonnull(1, 2))) {
156	/* paranoid */ verify( ! __preemption_enabled() );
157	/* paranoid */ verify( ready_schedule_islocked() );
158	/* paranoid */ verify( ctx->cq.lock == true );
159
160	const __u32 mask = *ctx->cq.mask;
161	const __u32 num = *ctx->cq.num;
162	unsigned long long ts_prev = ctx->cq.ts;
163	unsigned long long ts_next;
164
165	// We might need to do this multiple times if more events completed than can fit in the queue.
166	for() {
167	// re-read the head and tail in case it already changed.
168	const __u32 head = *ctx->cq.head;
169	const __u32 tail = *ctx->cq.tail;
170	const __u32 count = tail - head;
171	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
172
173	for(i; count) {
174	unsigned idx = (head + i) & mask;
175	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
176
177	/* paranoid */ verify(&cqe);
178
179	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
180	// __cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
181
182	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
183	}
184
185	ts_next = ctx->cq.ts = rdtscl();
186
187	// Mark to the kernel that the cqe has been seen
188	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
189	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
190	ctx->proc->idle_wctx.drain_time = ts_next;
191
192	if(likely(count < num)) break;
193
194	ioring_syscsll( *ctx, 0, IORING_ENTER_GETEVENTS);
195	}
196
197	__cfadbg_print_safe(io, "Kernel I/O : %u completed age %llu\n", count, ts_next);
198	/* paranoid */ verify( ready_schedule_islocked() );
199	/* paranoid */ verify( ! __preemption_enabled() );
200
201	__atomic_unlock(&ctx->cq.lock);
202
203	touch_tsc( cltr->sched.io.tscs, ctx->cq.id, ts_prev, ts_next );
204
205	return true;
206	}
207
208	bool __cfa_io_drain( processor * proc ) {
209	bool local = false;
210	bool remote = false;
211
212	ready_schedule_lock();
213
214	cluster * const cltr = proc->cltr;
215	$io_context * const ctx = proc->io.ctx;
216	/* paranoid */ verify( cltr );
217	/* paranoid */ verify( ctx );
218
219	with(cltr->sched) {
220	const size_t ctxs_count = io.count;
221
222	/* paranoid */ verify( ready_schedule_islocked() );
223	/* paranoid */ verify( ! __preemption_enabled() );
224	/* paranoid */ verify( active_processor() == proc );
225	/* paranoid */ verify( __shard_factor.io > 0 );
226	/* paranoid */ verify( ctxs_count > 0 );
227	/* paranoid */ verify( ctx->cq.id < ctxs_count );
228
229	const unsigned this_cache = cache_id(cltr, ctx->cq.id / __shard_factor.io);
230	const unsigned long long ctsc = rdtscl();
231
232	if(proc->io.target == UINT_MAX) {
233	uint64_t chaos = __tls_rand();
234	unsigned ext = chaos & 0xff;
235	unsigned other = (chaos >> 8) % (ctxs_count);
236
237	if(ext < 3 \|\| __atomic_load_n(&caches[other / __shard_factor.io].id, __ATOMIC_RELAXED) == this_cache) {
238	proc->io.target = other;
239	}
240	}
241	else {
242	const unsigned target = proc->io.target;
243	/* paranoid */ verify( io.tscs[target].tv != ULLONG_MAX );
244	HELP: if(target < ctxs_count) {
245	const unsigned long long cutoff = calc_cutoff(ctsc, ctx->cq.id, ctxs_count, io.data, io.tscs, __shard_factor.io);
246	const unsigned long long age = moving_average(ctsc, io.tscs[target].tv, io.tscs[target].ma);
247	__cfadbg_print_safe(io, "Kernel I/O: Help attempt on %u from %u, age %'llu vs cutoff %'llu, %s\n", target, ctx->cq.id, age, cutoff, age > cutoff ? "yes" : "no");
248	if(age <= cutoff) break HELP;
249
250	if(!try_acquire(io.data[target])) break HELP;
251
252	if(!__cfa_do_drain( io.data[target], cltr )) break HELP;
253
254	remote = true;
255	__STATS__( true, io.calls.helped++; )
256	}
257	proc->io.target = UINT_MAX;
258	}
259	}
260
261
262	// Drain the local queue
263	if(try_acquire( proc->io.ctx )) {
264	local = __cfa_do_drain( proc->io.ctx, cltr );
265	}
266
267	/* paranoid */ verify( ready_schedule_islocked() );
268	/* paranoid */ verify( ! __preemption_enabled() );
269	/* paranoid */ verify( active_processor() == proc );
270
271	ready_schedule_unlock();
272	return local \|\| remote;
273	}
274
275	bool __cfa_io_flush( processor * proc ) {
276	/* paranoid */ verify( ! __preemption_enabled() );
277	/* paranoid */ verify( proc );
278	/* paranoid */ verify( proc->io.ctx );
279
280	$io_context & ctx = *proc->io.ctx;
281
282	__ioarbiter_flush( ctx );
283
284	if(ctx.sq.to_submit != 0) {
285	ioring_syscsll(ctx, 0, 0);
286
287	}
288
289	return __cfa_io_drain( proc );
290	}
291
292	//=============================================================================================
293	// I/O Submissions
294	//=============================================================================================
295
296	// Submition steps :
297	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
298	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
299	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
300	// need to write an allocator that allows allocating concurrently.
301	//
302	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
303	//
304	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
305	// needs to arrive to two concensus at the same time:
306	// A - The order in which entries are listed in the array: no two threads must pick the
307	// same index for their entries
308	// B - When can the tail be update for the kernel. EVERY entries in the array between
309	// head and tail must be fully filled and shouldn't ever be touched again.
310	//
311	//=============================================================================================
312	// Allocation
313	// for user's convenience fill the sqes from the indexes
314	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
315	struct io_uring_sqe * sqes = ctx->sq.sqes;
316	for(i; want) {
317	// __cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
318	out_sqes[i] = &sqes[idxs[i]];
319	}
320	}
321
322	// Try to directly allocate from the a given context
323	// Not thread-safe
324	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
325	__sub_ring_t & sq = ctx->sq;
326	const __u32 mask = *sq.mask;
327	__u32 fhead = sq.free_ring.head; // get the current head of the queue
328	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
329
330	// If we don't have enough sqes, fail
331	if((ftail - fhead) < want) { return false; }
332
333	// copy all the indexes we want from the available list
334	for(i; want) {
335	// __cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
336	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
337	}
338
339	// Advance the head to mark the indexes as consumed
340	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
341
342	// return success
343	return true;
344	}
345
346	// Allocate an submit queue entry.
347	// The kernel cannot see these entries until they are submitted, but other threads must be
348	// able to see which entries can be used and which are already un used by an other thread
349	// for convenience, return both the index and the pointer to the sqe
350	// sqe == &sqes[idx]
351	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) libcfa_public {
352	// __cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
353
354	disable_interrupts();
355	processor * proc = __cfaabi_tls.this_processor;
356	$io_context * ctx = proc->io.ctx;
357	/* paranoid */ verify( __cfaabi_tls.this_processor );
358	/* paranoid */ verify( ctx );
359
360	// __cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
361
362	// We can proceed to the fast path
363	if( __alloc(ctx, idxs, want) ) {
364	// Allocation was successful
365	__STATS__( true, io.alloc.fast += 1; )
366	enable_interrupts();
367
368	// __cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
369
370	__fill( sqes, want, idxs, ctx );
371	return ctx;
372	}
373	// The fast path failed, fallback
374	__STATS__( true, io.alloc.fail += 1; )
375
376	// Fast path failed, fallback on arbitration
377	__STATS__( true, io.alloc.slow += 1; )
378	enable_interrupts();
379
380	$io_arbiter * ioarb = proc->cltr->io.arbiter;
381	/* paranoid */ verify( ioarb );
382
383	// __cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
384
385	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
386
387	// __cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
388
389	__fill( sqes, want, idxs,ret );
390	return ret;
391	}
392
393	//=============================================================================================
394	// submission
395	static inline void __submit_only( struct $io_context * ctx, __u32 idxs[], __u32 have) {
396	// We can proceed to the fast path
397	// Get the right objects
398	__sub_ring_t & sq = ctx->sq;
399	const __u32 mask = *sq.mask;
400	__u32 tail = *sq.kring.tail;
401
402	// Add the sqes to the array
403	for( i; have ) {
404	// __cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
405	sq.kring.array[ (tail + i) & mask ] = idxs[i];
406	}
407
408	// Make the sqes visible to the submitter
409	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
410	sq.to_submit += have;
411
412	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_RELAXED);
413	__atomic_store_n(&ctx->proc->io.dirty , true, __ATOMIC_RELAXED);
414	}
415
416	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
417	__sub_ring_t & sq = ctx->sq;
418	__submit_only(ctx, idxs, have);
419
420	if(sq.to_submit > 30) {
421	__tls_stats()->io.flush.full++;
422	__cfa_io_flush( ctx->proc );
423	}
424	if(!lazy) {
425	__tls_stats()->io.flush.eager++;
426	__cfa_io_flush( ctx->proc );
427	}
428	}
429
430	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) libcfa_public {
431	// __cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
432
433	disable_interrupts();
434	processor * proc = __cfaabi_tls.this_processor;
435	$io_context * ctx = proc->io.ctx;
436	/* paranoid */ verify( __cfaabi_tls.this_processor );
437	/* paranoid */ verify( ctx );
438
439	// Can we proceed to the fast path
440	if( ctx == inctx ) // We have the right instance?
441	{
442	__submit(ctx, idxs, have, lazy);
443
444	// Mark the instance as no longer in-use, re-enable interrupts and return
445	__STATS__( true, io.submit.fast += 1; )
446	enable_interrupts();
447
448	// __cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
449	return;
450	}
451
452	// Fast path failed, fallback on arbitration
453	__STATS__( true, io.submit.slow += 1; )
454	enable_interrupts();
455
456	// __cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
457
458	__ioarbiter_submit(inctx, idxs, have, lazy);
459	}
460
461	//=============================================================================================
462	// Flushing
463	// Go through the ring's submit queue and release everything that has already been consumed
464	// by io_uring
465	// This cannot be done by multiple threads
466	static __u32 __release_sqes( struct $io_context & ctx ) {
467	const __u32 mask = *ctx.sq.mask;
468
469	__attribute__((unused))
470	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
471	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
472	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
473
474	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
475
476	// the 3 fields are organized like this diagram
477	// except it's are ring
478	// ---+--------+--------+----
479	// ---+--------+--------+----
480	// ^ ^ ^
481	// phead chead ctail
482
483	// make sure ctail doesn't wrap around and reach phead
484	/* paranoid */ verify(
485	(ctail >= chead && chead >= phead)
486	\|\| (chead >= phead && phead >= ctail)
487	\|\| (phead >= ctail && ctail >= chead)
488	);
489
490	// find the range we need to clear
491	__u32 count = chead - phead;
492
493	if(count == 0) {
494	return 0;
495	}
496
497	// We acquired an previous-head/current-head range
498	// go through the range and release the sqes
499	for( i; count ) {
500	// __cfadbg_print_safe(io, "Kernel I/O : release loop\n");
501	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
502	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
503	}
504
505	ctx.sq.kring.released = chead; // note up to were we processed
506	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
507
508	__ioarbiter_notify(ctx);
509
510	return count;
511	}
512
513	//=============================================================================================
514	// I/O Arbiter
515	//=============================================================================================
516	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
517	bool was_empty;
518
519	// Lock the list, it's not thread safe
520	lock( queue.lock __cfaabi_dbg_ctx2 );
521	{
522	was_empty = empty(queue.queue);
523
524	// Add our request to the list
525	add( queue.queue, item );
526
527	// Mark as pending
528	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
529	}
530	unlock( queue.lock );
531
532	return was_empty;
533	}
534
535	static inline bool empty(__outstanding_io_queue & queue ) {
536	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
537	}
538
539	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
540	// __cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
541
542	__STATS__( false, io.alloc.block += 1; )
543
544	// No one has any resources left, wait for something to finish
545	// We need to add ourself to a list of pending allocs and wait for an answer
546	__pending_alloc pa;
547	pa.idxs = idxs;
548	pa.want = want;
549
550	enqueue(this.pending, (__outstanding_io&)pa);
551
552	wait( pa.sem );
553
554	return pa.ctx;
555
556	}
557
558	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
559	/* paranoid */ verify( !empty(this.pending.queue) );
560
561	lock( this.pending.lock __cfaabi_dbg_ctx2 );
562	{
563	while( !empty(this.pending.queue) ) {
564	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
565	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
566	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
567
568	if( have > pa.want ) goto DONE;
569	drop( this.pending.queue );
570
571	/* paranoid */__attribute__((unused)) bool ret =
572
573	__alloc(ctx, pa.idxs, pa.want);
574
575	/* paranoid */ verify( ret );
576
577	pa.ctx = ctx;
578
579	post( pa.sem );
580	}
581
582	this.pending.empty = true;
583	DONE:;
584	}
585	unlock( this.pending.lock );
586	}
587
588	static void __ioarbiter_notify( $io_context & ctx ) {
589	if(!empty( ctx.arbiter->pending )) {
590	__ioarbiter_notify( *ctx.arbiter, &ctx );
591	}
592	}
593
594	// Simply append to the pending
595	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
596	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
597
598	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
599
600	__external_io ei;
601	ei.idxs = idxs;
602	ei.have = have;
603	ei.lazy = lazy;
604
605	bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
606
607	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_SEQ_CST);
608
609	if( we ) {
610	sigval_t value = { PREEMPT_IO };
611	pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
612	}
613
614	wait( ei.sem );
615
616	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
617	}
618
619	static void __ioarbiter_flush( $io_context & ctx ) {
620	if(!empty( ctx.ext_sq )) {
621	__STATS__( false, io.flush.external += 1; )
622
623	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
624
625	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
626	{
627	while( !empty(ctx.ext_sq.queue) ) {
628	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
629
630	__submit_only(&ctx, ei.idxs, ei.have);
631
632	post( ei.sem );
633	}
634
635	ctx.ext_sq.empty = true;
636	}
637	unlock(ctx.ext_sq.lock );
638	}
639	}
640
641	#if defined(CFA_WITH_IO_URING_IDLE)
642	bool __kernel_read(processor * proc, io_future_t & future, iovec & iov, int fd) {
643	$io_context * ctx = proc->io.ctx;
644	/* paranoid */ verify( ! __preemption_enabled() );
645	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
646	/* paranoid */ verify( ctx );
647
648	__u32 idx;
649	struct io_uring_sqe * sqe;
650
651	// We can proceed to the fast path
652	if( !__alloc(ctx, &idx, 1) ) {
653	/* paranoid */ verify( false ); // for now check if this happens, next time just abort the sleep.
654	return false;
655	}
656
657	// Allocation was successful
658	__fill( &sqe, 1, &idx, ctx );
659
660	sqe->user_data = (uintptr_t)&future;
661	sqe->flags = 0;
662	sqe->fd = fd;
663	sqe->off = 0;
664	sqe->ioprio = 0;
665	sqe->fsync_flags = 0;
666	sqe->__pad2[0] = 0;
667	sqe->__pad2[1] = 0;
668	sqe->__pad2[2] = 0;
669
670	#if defined(CFA_HAVE_IORING_OP_READ)
671	sqe->opcode = IORING_OP_READ;
672	sqe->addr = (uint64_t)iov.iov_base;
673	sqe->len = iov.iov_len;
674	#elif defined(CFA_HAVE_READV) && defined(CFA_HAVE_IORING_OP_READV)
675	sqe->opcode = IORING_OP_READV;
676	sqe->addr = (uintptr_t)&iov;
677	sqe->len = 1;
678	#else
679	#error CFA_WITH_IO_URING_IDLE but none of CFA_HAVE_READV, CFA_HAVE_IORING_OP_READV or CFA_HAVE_IORING_OP_READ defined
680	#endif
681
682	asm volatile("": : :"memory");
683
684	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
685	__submit_only( ctx, &idx, 1 );
686
687	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
688	/* paranoid */ verify( ! __preemption_enabled() );
689
690	return true;
691	}
692
693	void __cfa_io_idle( processor * proc ) {
694	iovec iov;
695	__atomic_acquire( &proc->io.ctx->cq.lock );
696
697	__attribute__((used)) volatile bool was_reset = false;
698
699	with( proc->idle_wctx) {
700
701	// Do we already have a pending read
702	if(available(*ftr)) {
703	// There is no pending read, we need to add one
704	reset(*ftr);
705
706	iov.iov_base = rdbuf;
707	iov.iov_len = sizeof(eventfd_t);
708	__kernel_read(proc, *ftr, iov, evfd );
709	ftr->result = 0xDEADDEAD;
710	((eventfd_t )rdbuf) = 0xDEADDEADDEADDEAD;
711	was_reset = true;
712	}
713	}
714
715	if( !__atomic_load_n( &proc->do_terminate, __ATOMIC_SEQ_CST ) ) {
716	__ioarbiter_flush( *proc->io.ctx );
717	proc->idle_wctx.sleep_time = rdtscl();
718	ioring_syscsll( *proc->io.ctx, 1, IORING_ENTER_GETEVENTS);
719	}
720
721	ready_schedule_lock();
722	__cfa_do_drain( proc->io.ctx, proc->cltr );
723	ready_schedule_unlock();
724
725	asm volatile ("" :: "m" (was_reset));
726	}
727	#endif
728	#endif

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