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io.cfa@ 2377ca2

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ADT ast-experimental enum pthread-emulation qualifiedEnum

Last change on this file since 2377ca2 was 54c1196, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
Added io helping stats
Property mode set to `100644`
File size: 19.8 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 bool __cfa_do_drain( $io_context * ctx, cluster * cltr ) {
97	/* paranoid */ verify( ! __preemption_enabled() );
98	/* paranoid */ verify( ready_schedule_islocked() );
99	/* paranoid */ verify( ctx );
100
101	const __u32 mask = *ctx->cq.mask;
102
103
104	{
105	const __u32 head = *ctx->cq.head;
106	const __u32 tail = *ctx->cq.tail;
107
108	if(head == tail) return false;
109	}
110
111	// Drain the queue
112	if(!__atomic_try_acquire(&ctx->cq.lock)) {
113	__STATS__( false, io.calls.locked++; )
114	return false;
115	}
116
117	unsigned long long ts_prev = ctx->cq.ts;
118
119	// re-read the head and tail in case it already changed.
120	const __u32 head = *ctx->cq.head;
121	const __u32 tail = *ctx->cq.tail;
122	const __u32 count = tail - head;
123	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
124
125	for(i; count) {
126	unsigned idx = (head + i) & mask;
127	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
128
129	/* paranoid */ verify(&cqe);
130
131	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
132	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
133
134	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
135	}
136
137	__cfadbg_print_safe(io, "Kernel I/O : %u completed\n", count);
138	unsigned long long ts_next = ctx->cq.ts = rdtscl();
139
140	// Mark to the kernel that the cqe has been seen
141	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
142	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
143
144	/* paranoid */ verify( ready_schedule_islocked() );
145	/* paranoid */ verify( ! __preemption_enabled() );
146
147	__atomic_unlock(&ctx->cq.lock);
148
149	touch_tsc( cltr->sched.io.tscs, ctx->cq.id, ts_prev, ts_next );
150
151	return true;
152	}
153
154	bool __cfa_io_drain( processor * proc ) {
155	bool local = false;
156	bool remote = false;
157
158	cluster * const cltr = proc->cltr;
159	$io_context * const ctx = proc->io.ctx;
160	/* paranoid */ verify( cltr );
161	/* paranoid */ verify( ctx );
162
163	with(cltr->sched) {
164	const size_t ctxs_count = io.count;
165
166	/* paranoid */ verify( ready_schedule_islocked() );
167	/* paranoid */ verify( ! __preemption_enabled() );
168	/* paranoid */ verify( active_processor() == proc );
169	/* paranoid */ verify( __shard_factor.io > 0 );
170	/* paranoid */ verify( ctxs_count > 0 );
171	/* paranoid */ verify( ctx->cq.id < ctxs_count );
172
173	const unsigned this_cache = cache_id(cltr, ctx->cq.id / __shard_factor.io);
174	const unsigned long long ctsc = rdtscl();
175
176	if(proc->io.target == MAX) {
177	uint64_t chaos = __tls_rand();
178	unsigned ext = chaos & 0xff;
179	unsigned other = (chaos >> 8) % (ctxs_count);
180
181	if(ext < 3 \|\| __atomic_load_n(&caches[other / __shard_factor.io].id, __ATOMIC_RELAXED) == this_cache) {
182	proc->io.target = other;
183	}
184	}
185	else {
186	const unsigned target = proc->io.target;
187	/* paranoid */ verify( io.tscs[target].tv != MAX );
188	if(target < ctxs_count) {
189	const unsigned long long cutoff = calc_cutoff(ctsc, ctx->cq.id, ctxs_count, io.data, io.tscs, __shard_factor.io);
190	const unsigned long long age = moving_average(ctsc, io.tscs[target].tv, io.tscs[target].ma);
191	// __cfadbg_print_safe(ready_queue, "Kernel : Help attempt on %u from %u, age %'llu vs cutoff %'llu, %s\n", target, this, age, cutoff, age > cutoff ? "yes" : "no");
192	if(age > cutoff) {
193	remote = __cfa_do_drain( io.data[target], cltr );
194	if(remote) __STATS__( false, io.calls.helped++; )
195	}
196	}
197	proc->io.target = MAX;
198	}
199	}
200
201
202	// Drain the local queue
203	local = __cfa_do_drain( proc->io.ctx, cltr );
204
205	/* paranoid */ verify( ready_schedule_islocked() );
206	/* paranoid */ verify( ! __preemption_enabled() );
207	/* paranoid */ verify( active_processor() == proc );
208	return local \|\| remote;
209	}
210
211	bool __cfa_io_flush( processor * proc, int min_comp ) {
212	/* paranoid */ verify( ! __preemption_enabled() );
213	/* paranoid */ verify( proc );
214	/* paranoid */ verify( proc->io.ctx );
215
216	cluster * cltr = proc->cltr;
217	$io_context & ctx = *proc->io.ctx;
218
219	__ioarbiter_flush( ctx );
220
221	if(ctx.sq.to_submit != 0 \|\| min_comp > 0) {
222
223	__STATS__( true, io.calls.flush++; )
224	int ret = syscall( __NR_io_uring_enter, ctx.fd, ctx.sq.to_submit, min_comp, min_comp > 0 ? IORING_ENTER_GETEVENTS : 0, (sigset_t *)0p, _NSIG / 8);
225	if( ret < 0 ) {
226	switch((int)errno) {
227	case EAGAIN:
228	case EINTR:
229	case EBUSY:
230	// Update statistics
231	__STATS__( false, io.calls.errors.busy ++; )
232	return false;
233	default:
234	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
235	}
236	}
237
238	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring %d\n", ret, ctx.fd);
239	__STATS__( true, io.calls.submitted += ret; )
240	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
241	/* paranoid */ verify( ctx.sq.to_submit >= ret );
242
243	ctx.sq.to_submit -= ret;
244
245	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
246
247	// Release the consumed SQEs
248	__release_sqes( ctx );
249
250	/* paranoid */ verify( ! __preemption_enabled() );
251
252	__atomic_store_n(&ctx.proc->io.pending, false, __ATOMIC_RELAXED);
253	}
254
255	ready_schedule_lock();
256	bool ret = __cfa_io_drain( proc );
257	ready_schedule_unlock();
258	return ret;
259	}
260
261	//=============================================================================================
262	// I/O Submissions
263	//=============================================================================================
264
265	// Submition steps :
266	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
267	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
268	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
269	// need to write an allocator that allows allocating concurrently.
270	//
271	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
272	//
273	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
274	// needs to arrive to two concensus at the same time:
275	// A - The order in which entries are listed in the array: no two threads must pick the
276	// same index for their entries
277	// B - When can the tail be update for the kernel. EVERY entries in the array between
278	// head and tail must be fully filled and shouldn't ever be touched again.
279	//
280	//=============================================================================================
281	// Allocation
282	// for user's convenience fill the sqes from the indexes
283	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
284	struct io_uring_sqe * sqes = ctx->sq.sqes;
285	for(i; want) {
286	__cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
287	out_sqes[i] = &sqes[idxs[i]];
288	}
289	}
290
291	// Try to directly allocate from the a given context
292	// Not thread-safe
293	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
294	__sub_ring_t & sq = ctx->sq;
295	const __u32 mask = *sq.mask;
296	__u32 fhead = sq.free_ring.head; // get the current head of the queue
297	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
298
299	// If we don't have enough sqes, fail
300	if((ftail - fhead) < want) { return false; }
301
302	// copy all the indexes we want from the available list
303	for(i; want) {
304	__cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
305	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
306	}
307
308	// Advance the head to mark the indexes as consumed
309	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
310
311	// return success
312	return true;
313	}
314
315	// Allocate an submit queue entry.
316	// The kernel cannot see these entries until they are submitted, but other threads must be
317	// able to see which entries can be used and which are already un used by an other thread
318	// for convenience, return both the index and the pointer to the sqe
319	// sqe == &sqes[idx]
320	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) {
321	__cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
322
323	disable_interrupts();
324	processor * proc = __cfaabi_tls.this_processor;
325	$io_context * ctx = proc->io.ctx;
326	/* paranoid */ verify( __cfaabi_tls.this_processor );
327	/* paranoid */ verify( ctx );
328
329	__cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
330
331	// We can proceed to the fast path
332	if( __alloc(ctx, idxs, want) ) {
333	// Allocation was successful
334	__STATS__( true, io.alloc.fast += 1; )
335	enable_interrupts();
336
337	__cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
338
339	__fill( sqes, want, idxs, ctx );
340	return ctx;
341	}
342	// The fast path failed, fallback
343	__STATS__( true, io.alloc.fail += 1; )
344
345	// Fast path failed, fallback on arbitration
346	__STATS__( true, io.alloc.slow += 1; )
347	enable_interrupts();
348
349	$io_arbiter * ioarb = proc->cltr->io.arbiter;
350	/* paranoid */ verify( ioarb );
351
352	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
353
354	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
355
356	__cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
357
358	__fill( sqes, want, idxs,ret );
359	return ret;
360	}
361
362	//=============================================================================================
363	// submission
364	static inline void __submit_only( struct $io_context * ctx, __u32 idxs[], __u32 have) {
365	// We can proceed to the fast path
366	// Get the right objects
367	__sub_ring_t & sq = ctx->sq;
368	const __u32 mask = *sq.mask;
369	__u32 tail = *sq.kring.tail;
370
371	// Add the sqes to the array
372	for( i; have ) {
373	__cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
374	sq.kring.array[ (tail + i) & mask ] = idxs[i];
375	}
376
377	// Make the sqes visible to the submitter
378	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
379	sq.to_submit += have;
380
381	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_RELAXED);
382	__atomic_store_n(&ctx->proc->io.dirty , true, __ATOMIC_RELAXED);
383	}
384
385	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
386	__sub_ring_t & sq = ctx->sq;
387	__submit_only(ctx, idxs, have);
388
389	if(sq.to_submit > 30) {
390	__tls_stats()->io.flush.full++;
391	__cfa_io_flush( ctx->proc, 0 );
392	}
393	if(!lazy) {
394	__tls_stats()->io.flush.eager++;
395	__cfa_io_flush( ctx->proc, 0 );
396	}
397	}
398
399	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) {
400	__cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
401
402	disable_interrupts();
403	processor * proc = __cfaabi_tls.this_processor;
404	$io_context * ctx = proc->io.ctx;
405	/* paranoid */ verify( __cfaabi_tls.this_processor );
406	/* paranoid */ verify( ctx );
407
408	// Can we proceed to the fast path
409	if( ctx == inctx ) // We have the right instance?
410	{
411	__submit(ctx, idxs, have, lazy);
412
413	// Mark the instance as no longer in-use, re-enable interrupts and return
414	__STATS__( true, io.submit.fast += 1; )
415	enable_interrupts();
416
417	__cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
418	return;
419	}
420
421	// Fast path failed, fallback on arbitration
422	__STATS__( true, io.submit.slow += 1; )
423	enable_interrupts();
424
425	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
426
427	__ioarbiter_submit(inctx, idxs, have, lazy);
428	}
429
430	//=============================================================================================
431	// Flushing
432	// Go through the ring's submit queue and release everything that has already been consumed
433	// by io_uring
434	// This cannot be done by multiple threads
435	static __u32 __release_sqes( struct $io_context & ctx ) {
436	const __u32 mask = *ctx.sq.mask;
437
438	__attribute__((unused))
439	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
440	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
441	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
442
443	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
444
445	// the 3 fields are organized like this diagram
446	// except it's are ring
447	// ---+--------+--------+----
448	// ---+--------+--------+----
449	// ^ ^ ^
450	// phead chead ctail
451
452	// make sure ctail doesn't wrap around and reach phead
453	/* paranoid */ verify(
454	(ctail >= chead && chead >= phead)
455	\|\| (chead >= phead && phead >= ctail)
456	\|\| (phead >= ctail && ctail >= chead)
457	);
458
459	// find the range we need to clear
460	__u32 count = chead - phead;
461
462	if(count == 0) {
463	return 0;
464	}
465
466	// We acquired an previous-head/current-head range
467	// go through the range and release the sqes
468	for( i; count ) {
469	__cfadbg_print_safe(io, "Kernel I/O : release loop\n");
470	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
471	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
472	}
473
474	ctx.sq.kring.released = chead; // note up to were we processed
475	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
476
477	__ioarbiter_notify(ctx);
478
479	return count;
480	}
481
482	//=============================================================================================
483	// I/O Arbiter
484	//=============================================================================================
485	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
486	bool was_empty;
487
488	// Lock the list, it's not thread safe
489	lock( queue.lock __cfaabi_dbg_ctx2 );
490	{
491	was_empty = empty(queue.queue);
492
493	// Add our request to the list
494	add( queue.queue, item );
495
496	// Mark as pending
497	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
498	}
499	unlock( queue.lock );
500
501	return was_empty;
502	}
503
504	static inline bool empty(__outstanding_io_queue & queue ) {
505	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
506	}
507
508	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
509	__cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
510
511	__STATS__( false, io.alloc.block += 1; )
512
513	// No one has any resources left, wait for something to finish
514	// We need to add ourself to a list of pending allocs and wait for an answer
515	__pending_alloc pa;
516	pa.idxs = idxs;
517	pa.want = want;
518
519	enqueue(this.pending, (__outstanding_io&)pa);
520
521	wait( pa.sem );
522
523	return pa.ctx;
524
525	}
526
527	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
528	/* paranoid */ verify( !empty(this.pending.queue) );
529
530	lock( this.pending.lock __cfaabi_dbg_ctx2 );
531	{
532	while( !empty(this.pending.queue) ) {
533	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
534	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
535	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
536
537	if( have > pa.want ) goto DONE;
538	drop( this.pending.queue );
539
540	/* paranoid */__attribute__((unused)) bool ret =
541
542	__alloc(ctx, pa.idxs, pa.want);
543
544	/* paranoid */ verify( ret );
545
546	pa.ctx = ctx;
547
548	post( pa.sem );
549	}
550
551	this.pending.empty = true;
552	DONE:;
553	}
554	unlock( this.pending.lock );
555	}
556
557	static void __ioarbiter_notify( $io_context & ctx ) {
558	if(!empty( ctx.arbiter->pending )) {
559	__ioarbiter_notify( *ctx.arbiter, &ctx );
560	}
561	}
562
563	// Simply append to the pending
564	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
565	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
566
567	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
568
569	__external_io ei;
570	ei.idxs = idxs;
571	ei.have = have;
572	ei.lazy = lazy;
573
574	bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
575
576	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_SEQ_CST);
577
578	if( we ) {
579	sigval_t value = { PREEMPT_IO };
580	pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
581	}
582
583	wait( ei.sem );
584
585	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
586	}
587
588	static void __ioarbiter_flush( $io_context & ctx ) {
589	if(!empty( ctx.ext_sq )) {
590	__STATS__( false, io.flush.external += 1; )
591
592	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
593
594	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
595	{
596	while( !empty(ctx.ext_sq.queue) ) {
597	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
598
599	__submit_only(&ctx, ei.idxs, ei.have);
600
601	post( ei.sem );
602	}
603
604	ctx.ext_sq.empty = true;
605	}
606	unlock(ctx.ext_sq.lock );
607	}
608	}
609
610	#if defined(CFA_WITH_IO_URING_IDLE)
611	bool __kernel_read(processor * proc, io_future_t & future, iovec & iov, int fd) {
612	$io_context * ctx = proc->io.ctx;
613	/* paranoid */ verify( ! __preemption_enabled() );
614	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
615	/* paranoid */ verify( ctx );
616
617	__u32 idx;
618	struct io_uring_sqe * sqe;
619
620	// We can proceed to the fast path
621	if( !__alloc(ctx, &idx, 1) ) return false;
622
623	// Allocation was successful
624	__fill( &sqe, 1, &idx, ctx );
625
626	sqe->user_data = (uintptr_t)&future;
627	sqe->flags = 0;
628	sqe->fd = fd;
629	sqe->off = 0;
630	sqe->ioprio = 0;
631	sqe->fsync_flags = 0;
632	sqe->__pad2[0] = 0;
633	sqe->__pad2[1] = 0;
634	sqe->__pad2[2] = 0;
635
636	#if defined(CFA_HAVE_IORING_OP_READ)
637	sqe->opcode = IORING_OP_READ;
638	sqe->addr = (uint64_t)iov.iov_base;
639	sqe->len = iov.iov_len;
640	#elif defined(CFA_HAVE_READV) && defined(CFA_HAVE_IORING_OP_READV)
641	sqe->opcode = IORING_OP_READV;
642	sqe->addr = (uintptr_t)&iov;
643	sqe->len = 1;
644	#else
645	#error CFA_WITH_IO_URING_IDLE but none of CFA_HAVE_READV, CFA_HAVE_IORING_OP_READV or CFA_HAVE_IORING_OP_READ defined
646	#endif
647
648	asm volatile("": : :"memory");
649
650	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
651	__submit( ctx, &idx, 1, true );
652
653	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
654	/* paranoid */ verify( ! __preemption_enabled() );
655
656	return true;
657	}
658	#endif
659	#endif

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