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io.cfa @ 108345a

ADTast-experimentalpthread-emulationqualifiedEnum

Last change on this file since 108345a was 108345a, checked in by Thierry Delisle <tdelisle@…>, 2 years ago
visbility for io
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File size: 21.4 KB

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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	unsigned long long ts_prev = ctx->cq.ts;
162
163	// re-read the head and tail in case it already changed.
164	const __u32 head = *ctx->cq.head;
165	const __u32 tail = *ctx->cq.tail;
166	const __u32 count = tail - head;
167	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
168
169	for(i; count) {
170	unsigned idx = (head + i) & mask;
171	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
172
173	/* paranoid */ verify(&cqe);
174
175	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
176	// __cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
177
178	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
179	}
180
181	unsigned long long ts_next = ctx->cq.ts = rdtscl();
182
183	// Mark to the kernel that the cqe has been seen
184	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
185	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
186	ctx->proc->idle_wctx.drain_time = ts_next;
187
188	__cfadbg_print_safe(io, "Kernel I/O : %u completed age %llu\n", count, ts_next);
189	/* paranoid */ verify( ready_schedule_islocked() );
190	/* paranoid */ verify( ! __preemption_enabled() );
191
192	__atomic_unlock(&ctx->cq.lock);
193
194	touch_tsc( cltr->sched.io.tscs, ctx->cq.id, ts_prev, ts_next );
195
196	return true;
197	}
198
199	bool __cfa_io_drain( processor * proc ) {
200	bool local = false;
201	bool remote = false;
202
203	ready_schedule_lock();
204
205	cluster * const cltr = proc->cltr;
206	$io_context * const ctx = proc->io.ctx;
207	/* paranoid */ verify( cltr );
208	/* paranoid */ verify( ctx );
209
210	with(cltr->sched) {
211	const size_t ctxs_count = io.count;
212
213	/* paranoid */ verify( ready_schedule_islocked() );
214	/* paranoid */ verify( ! __preemption_enabled() );
215	/* paranoid */ verify( active_processor() == proc );
216	/* paranoid */ verify( __shard_factor.io > 0 );
217	/* paranoid */ verify( ctxs_count > 0 );
218	/* paranoid */ verify( ctx->cq.id < ctxs_count );
219
220	const unsigned this_cache = cache_id(cltr, ctx->cq.id / __shard_factor.io);
221	const unsigned long long ctsc = rdtscl();
222
223	if(proc->io.target == MAX) {
224	uint64_t chaos = __tls_rand();
225	unsigned ext = chaos & 0xff;
226	unsigned other = (chaos >> 8) % (ctxs_count);
227
228	if(ext < 3 \|\| __atomic_load_n(&caches[other / __shard_factor.io].id, __ATOMIC_RELAXED) == this_cache) {
229	proc->io.target = other;
230	}
231	}
232	else {
233	const unsigned target = proc->io.target;
234	/* paranoid */ verify( io.tscs[target].tv != MAX );
235	HELP: if(target < ctxs_count) {
236	const unsigned long long cutoff = calc_cutoff(ctsc, ctx->cq.id, ctxs_count, io.data, io.tscs, __shard_factor.io);
237	const unsigned long long age = moving_average(ctsc, io.tscs[target].tv, io.tscs[target].ma);
238	__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");
239	if(age <= cutoff) break HELP;
240
241	if(!try_acquire(io.data[target])) break HELP;
242
243	if(!__cfa_do_drain( io.data[target], cltr )) break HELP;
244
245	remote = true;
246	__STATS__( true, io.calls.helped++; )
247	}
248	proc->io.target = MAX;
249	}
250	}
251
252
253	// Drain the local queue
254	if(try_acquire( proc->io.ctx )) {
255	local = __cfa_do_drain( proc->io.ctx, cltr );
256	}
257
258	/* paranoid */ verify( ready_schedule_islocked() );
259	/* paranoid */ verify( ! __preemption_enabled() );
260	/* paranoid */ verify( active_processor() == proc );
261
262	ready_schedule_unlock();
263	return local \|\| remote;
264	}
265
266	bool __cfa_io_flush( processor * proc ) {
267	/* paranoid */ verify( ! __preemption_enabled() );
268	/* paranoid */ verify( proc );
269	/* paranoid */ verify( proc->io.ctx );
270
271	$io_context & ctx = *proc->io.ctx;
272
273	__ioarbiter_flush( ctx );
274
275	if(ctx.sq.to_submit != 0) {
276	ioring_syscsll(ctx, 0, 0);
277
278	}
279
280	return __cfa_io_drain( proc );
281	}
282
283	//=============================================================================================
284	// I/O Submissions
285	//=============================================================================================
286
287	// Submition steps :
288	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
289	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
290	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
291	// need to write an allocator that allows allocating concurrently.
292	//
293	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
294	//
295	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
296	// needs to arrive to two concensus at the same time:
297	// A - The order in which entries are listed in the array: no two threads must pick the
298	// same index for their entries
299	// B - When can the tail be update for the kernel. EVERY entries in the array between
300	// head and tail must be fully filled and shouldn't ever be touched again.
301	//
302	//=============================================================================================
303	// Allocation
304	// for user's convenience fill the sqes from the indexes
305	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
306	struct io_uring_sqe * sqes = ctx->sq.sqes;
307	for(i; want) {
308	// __cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
309	out_sqes[i] = &sqes[idxs[i]];
310	}
311	}
312
313	// Try to directly allocate from the a given context
314	// Not thread-safe
315	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
316	__sub_ring_t & sq = ctx->sq;
317	const __u32 mask = *sq.mask;
318	__u32 fhead = sq.free_ring.head; // get the current head of the queue
319	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
320
321	// If we don't have enough sqes, fail
322	if((ftail - fhead) < want) { return false; }
323
324	// copy all the indexes we want from the available list
325	for(i; want) {
326	// __cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
327	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
328	}
329
330	// Advance the head to mark the indexes as consumed
331	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
332
333	// return success
334	return true;
335	}
336
337	// Allocate an submit queue entry.
338	// The kernel cannot see these entries until they are submitted, but other threads must be
339	// able to see which entries can be used and which are already un used by an other thread
340	// for convenience, return both the index and the pointer to the sqe
341	// sqe == &sqes[idx]
342	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) libcfa_public {
343	// __cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
344
345	disable_interrupts();
346	processor * proc = __cfaabi_tls.this_processor;
347	$io_context * ctx = proc->io.ctx;
348	/* paranoid */ verify( __cfaabi_tls.this_processor );
349	/* paranoid */ verify( ctx );
350
351	// __cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
352
353	// We can proceed to the fast path
354	if( __alloc(ctx, idxs, want) ) {
355	// Allocation was successful
356	__STATS__( true, io.alloc.fast += 1; )
357	enable_interrupts();
358
359	// __cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
360
361	__fill( sqes, want, idxs, ctx );
362	return ctx;
363	}
364	// The fast path failed, fallback
365	__STATS__( true, io.alloc.fail += 1; )
366
367	// Fast path failed, fallback on arbitration
368	__STATS__( true, io.alloc.slow += 1; )
369	enable_interrupts();
370
371	$io_arbiter * ioarb = proc->cltr->io.arbiter;
372	/* paranoid */ verify( ioarb );
373
374	// __cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
375
376	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
377
378	// __cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
379
380	__fill( sqes, want, idxs,ret );
381	return ret;
382	}
383
384	//=============================================================================================
385	// submission
386	static inline void __submit_only( struct $io_context * ctx, __u32 idxs[], __u32 have) {
387	// We can proceed to the fast path
388	// Get the right objects
389	__sub_ring_t & sq = ctx->sq;
390	const __u32 mask = *sq.mask;
391	__u32 tail = *sq.kring.tail;
392
393	// Add the sqes to the array
394	for( i; have ) {
395	// __cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
396	sq.kring.array[ (tail + i) & mask ] = idxs[i];
397	}
398
399	// Make the sqes visible to the submitter
400	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
401	sq.to_submit += have;
402
403	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_RELAXED);
404	__atomic_store_n(&ctx->proc->io.dirty , true, __ATOMIC_RELAXED);
405	}
406
407	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
408	__sub_ring_t & sq = ctx->sq;
409	__submit_only(ctx, idxs, have);
410
411	if(sq.to_submit > 30) {
412	__tls_stats()->io.flush.full++;
413	__cfa_io_flush( ctx->proc );
414	}
415	if(!lazy) {
416	__tls_stats()->io.flush.eager++;
417	__cfa_io_flush( ctx->proc );
418	}
419	}
420
421	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) libcfa_public {
422	// __cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
423
424	disable_interrupts();
425	processor * proc = __cfaabi_tls.this_processor;
426	$io_context * ctx = proc->io.ctx;
427	/* paranoid */ verify( __cfaabi_tls.this_processor );
428	/* paranoid */ verify( ctx );
429
430	// Can we proceed to the fast path
431	if( ctx == inctx ) // We have the right instance?
432	{
433	__submit(ctx, idxs, have, lazy);
434
435	// Mark the instance as no longer in-use, re-enable interrupts and return
436	__STATS__( true, io.submit.fast += 1; )
437	enable_interrupts();
438
439	// __cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
440	return;
441	}
442
443	// Fast path failed, fallback on arbitration
444	__STATS__( true, io.submit.slow += 1; )
445	enable_interrupts();
446
447	// __cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
448
449	__ioarbiter_submit(inctx, idxs, have, lazy);
450	}
451
452	//=============================================================================================
453	// Flushing
454	// Go through the ring's submit queue and release everything that has already been consumed
455	// by io_uring
456	// This cannot be done by multiple threads
457	static __u32 __release_sqes( struct $io_context & ctx ) {
458	const __u32 mask = *ctx.sq.mask;
459
460	__attribute__((unused))
461	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
462	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
463	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
464
465	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
466
467	// the 3 fields are organized like this diagram
468	// except it's are ring
469	// ---+--------+--------+----
470	// ---+--------+--------+----
471	// ^ ^ ^
472	// phead chead ctail
473
474	// make sure ctail doesn't wrap around and reach phead
475	/* paranoid */ verify(
476	(ctail >= chead && chead >= phead)
477	\|\| (chead >= phead && phead >= ctail)
478	\|\| (phead >= ctail && ctail >= chead)
479	);
480
481	// find the range we need to clear
482	__u32 count = chead - phead;
483
484	if(count == 0) {
485	return 0;
486	}
487
488	// We acquired an previous-head/current-head range
489	// go through the range and release the sqes
490	for( i; count ) {
491	// __cfadbg_print_safe(io, "Kernel I/O : release loop\n");
492	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
493	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
494	}
495
496	ctx.sq.kring.released = chead; // note up to were we processed
497	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
498
499	__ioarbiter_notify(ctx);
500
501	return count;
502	}
503
504	//=============================================================================================
505	// I/O Arbiter
506	//=============================================================================================
507	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
508	bool was_empty;
509
510	// Lock the list, it's not thread safe
511	lock( queue.lock __cfaabi_dbg_ctx2 );
512	{
513	was_empty = empty(queue.queue);
514
515	// Add our request to the list
516	add( queue.queue, item );
517
518	// Mark as pending
519	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
520	}
521	unlock( queue.lock );
522
523	return was_empty;
524	}
525
526	static inline bool empty(__outstanding_io_queue & queue ) {
527	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
528	}
529
530	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
531	// __cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
532
533	__STATS__( false, io.alloc.block += 1; )
534
535	// No one has any resources left, wait for something to finish
536	// We need to add ourself to a list of pending allocs and wait for an answer
537	__pending_alloc pa;
538	pa.idxs = idxs;
539	pa.want = want;
540
541	enqueue(this.pending, (__outstanding_io&)pa);
542
543	wait( pa.sem );
544
545	return pa.ctx;
546
547	}
548
549	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
550	/* paranoid */ verify( !empty(this.pending.queue) );
551
552	lock( this.pending.lock __cfaabi_dbg_ctx2 );
553	{
554	while( !empty(this.pending.queue) ) {
555	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
556	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
557	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
558
559	if( have > pa.want ) goto DONE;
560	drop( this.pending.queue );
561
562	/* paranoid */__attribute__((unused)) bool ret =
563
564	__alloc(ctx, pa.idxs, pa.want);
565
566	/* paranoid */ verify( ret );
567
568	pa.ctx = ctx;
569
570	post( pa.sem );
571	}
572
573	this.pending.empty = true;
574	DONE:;
575	}
576	unlock( this.pending.lock );
577	}
578
579	static void __ioarbiter_notify( $io_context & ctx ) {
580	if(!empty( ctx.arbiter->pending )) {
581	__ioarbiter_notify( *ctx.arbiter, &ctx );
582	}
583	}
584
585	// Simply append to the pending
586	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
587	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
588
589	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
590
591	__external_io ei;
592	ei.idxs = idxs;
593	ei.have = have;
594	ei.lazy = lazy;
595
596	bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
597
598	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_SEQ_CST);
599
600	if( we ) {
601	sigval_t value = { PREEMPT_IO };
602	pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
603	}
604
605	wait( ei.sem );
606
607	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
608	}
609
610	static void __ioarbiter_flush( $io_context & ctx ) {
611	if(!empty( ctx.ext_sq )) {
612	__STATS__( false, io.flush.external += 1; )
613
614	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
615
616	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
617	{
618	while( !empty(ctx.ext_sq.queue) ) {
619	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
620
621	__submit_only(&ctx, ei.idxs, ei.have);
622
623	post( ei.sem );
624	}
625
626	ctx.ext_sq.empty = true;
627	}
628	unlock(ctx.ext_sq.lock );
629	}
630	}
631
632	#if defined(CFA_WITH_IO_URING_IDLE)
633	bool __kernel_read(processor * proc, io_future_t & future, iovec & iov, int fd) {
634	$io_context * ctx = proc->io.ctx;
635	/* paranoid */ verify( ! __preemption_enabled() );
636	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
637	/* paranoid */ verify( ctx );
638
639	__u32 idx;
640	struct io_uring_sqe * sqe;
641
642	// We can proceed to the fast path
643	if( !__alloc(ctx, &idx, 1) ) {
644	/* paranoid */ verify( false ); // for now check if this happens, next time just abort the sleep.
645	return false;
646	}
647
648	// Allocation was successful
649	__fill( &sqe, 1, &idx, ctx );
650
651	sqe->user_data = (uintptr_t)&future;
652	sqe->flags = 0;
653	sqe->fd = fd;
654	sqe->off = 0;
655	sqe->ioprio = 0;
656	sqe->fsync_flags = 0;
657	sqe->__pad2[0] = 0;
658	sqe->__pad2[1] = 0;
659	sqe->__pad2[2] = 0;
660
661	#if defined(CFA_HAVE_IORING_OP_READ)
662	sqe->opcode = IORING_OP_READ;
663	sqe->addr = (uint64_t)iov.iov_base;
664	sqe->len = iov.iov_len;
665	#elif defined(CFA_HAVE_READV) && defined(CFA_HAVE_IORING_OP_READV)
666	sqe->opcode = IORING_OP_READV;
667	sqe->addr = (uintptr_t)&iov;
668	sqe->len = 1;
669	#else
670	#error CFA_WITH_IO_URING_IDLE but none of CFA_HAVE_READV, CFA_HAVE_IORING_OP_READV or CFA_HAVE_IORING_OP_READ defined
671	#endif
672
673	asm volatile("": : :"memory");
674
675	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
676	__submit_only( ctx, &idx, 1 );
677
678	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
679	/* paranoid */ verify( ! __preemption_enabled() );
680
681	return true;
682	}
683
684	void __cfa_io_idle( processor * proc ) {
685	iovec iov;
686	__atomic_acquire( &proc->io.ctx->cq.lock );
687
688	__attribute__((used)) volatile bool was_reset = false;
689
690	with( proc->idle_wctx) {
691
692	// Do we already have a pending read
693	if(available(*ftr)) {
694	// There is no pending read, we need to add one
695	reset(*ftr);
696
697	iov.iov_base = rdbuf;
698	iov.iov_len = sizeof(eventfd_t);
699	__kernel_read(proc, *ftr, iov, evfd );
700	ftr->result = 0xDEADDEAD;
701	((eventfd_t )rdbuf) = 0xDEADDEADDEADDEAD;
702	was_reset = true;
703	}
704	}
705
706	if( !__atomic_load_n( &proc->do_terminate, __ATOMIC_SEQ_CST ) ) {
707	__ioarbiter_flush( *proc->io.ctx );
708	proc->idle_wctx.sleep_time = rdtscl();
709	ioring_syscsll( *proc->io.ctx, 1, IORING_ENTER_GETEVENTS);
710	}
711
712	ready_schedule_lock();
713	__cfa_do_drain( proc->io.ctx, proc->cltr );
714	ready_schedule_unlock();
715
716	asm volatile ("" :: "m" (was_reset));
717	}
718	#endif
719	#endif

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