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io.cfa@ 1a567d0

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ADT ast-experimental enum pthread-emulation qualifiedEnum

Last change on this file since 1a567d0 was 4479890, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
Implemented helping for io drain based on timestamps.
Property mode set to `100644`
File size: 19.6 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	// Drain the queue
102	unsigned head = *ctx->cq.head;
103	unsigned tail = *ctx->cq.tail;
104	const __u32 mask = *ctx->cq.mask;
105
106	__u32 count = tail - head;
107	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
108
109	if(count == 0) return false;
110
111	if(!__atomic_try_acquire(&ctx->cq.lock)) {
112	return false;
113	}
114
115	unsigned long long ts_prev = ctx->cq.ts;
116
117	for(i; count) {
118	unsigned idx = (head + i) & mask;
119	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
120
121	/* paranoid */ verify(&cqe);
122
123	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
124	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
125
126	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
127	}
128
129	__cfadbg_print_safe(io, "Kernel I/O : %u completed\n", count);
130	unsigned long long ts_next = ctx->cq.ts = rdtscl();
131
132	// Mark to the kernel that the cqe has been seen
133	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
134	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
135
136	/* paranoid */ verify( ready_schedule_islocked() );
137	/* paranoid */ verify( ! __preemption_enabled() );
138
139	__atomic_unlock(&ctx->cq.lock);
140
141	touch_tsc( cltr->sched.io.tscs, ctx->cq.id, ts_prev, ts_next );
142
143	return true;
144	}
145
146	bool __cfa_io_drain( processor * proc ) {
147	bool local = false;
148	bool remote = false;
149
150	cluster * const cltr = proc->cltr;
151	$io_context * const ctx = proc->io.ctx;
152	/* paranoid */ verify( cltr );
153	/* paranoid */ verify( ctx );
154
155	with(cltr->sched) {
156	const size_t ctxs_count = io.count;
157
158	/* paranoid */ verify( ready_schedule_islocked() );
159	/* paranoid */ verify( ! __preemption_enabled() );
160	/* paranoid */ verify( active_processor() == proc );
161	/* paranoid */ verify( __shard_factor.io > 0 );
162	/* paranoid */ verify( ctxs_count > 0 );
163	/* paranoid */ verify( ctx->cq.id < ctxs_count );
164
165	const unsigned this_cache = cache_id(cltr, ctx->cq.id / __shard_factor.io);
166	const unsigned long long ctsc = rdtscl();
167
168	if(proc->io.target == MAX) {
169	uint64_t chaos = __tls_rand();
170	unsigned ext = chaos & 0xff;
171	unsigned other = (chaos >> 8) % (ctxs_count);
172
173	if(ext < 3 \|\| __atomic_load_n(&caches[other / __shard_factor.io].id, __ATOMIC_RELAXED) == this_cache) {
174	proc->io.target = other;
175	}
176	}
177	else {
178	const unsigned target = proc->io.target;
179	/* paranoid */ verify( io.tscs[target].tv != MAX );
180	if(target < ctxs_count) {
181	const unsigned long long cutoff = calc_cutoff(ctsc, ctx->cq.id, ctxs_count, io.data, io.tscs, __shard_factor.io);
182	const unsigned long long age = moving_average(ctsc, io.tscs[target].tv, io.tscs[target].ma);
183	// __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");
184	if(age > cutoff) {
185	remote = __cfa_do_drain( io.data[target], cltr );
186	}
187	}
188	proc->io.target = MAX;
189	}
190	}
191
192
193	// Drain the local queue
194	local = __cfa_do_drain( proc->io.ctx, cltr );
195
196	/* paranoid */ verify( ready_schedule_islocked() );
197	/* paranoid */ verify( ! __preemption_enabled() );
198	/* paranoid */ verify( active_processor() == proc );
199	return local \|\| remote;
200	}
201
202	bool __cfa_io_flush( processor * proc, int min_comp ) {
203	/* paranoid */ verify( ! __preemption_enabled() );
204	/* paranoid */ verify( proc );
205	/* paranoid */ verify( proc->io.ctx );
206
207	cluster * cltr = proc->cltr;
208	$io_context & ctx = *proc->io.ctx;
209
210	__ioarbiter_flush( ctx );
211
212	if(ctx.sq.to_submit != 0 \|\| min_comp > 0) {
213
214	__STATS__( true, io.calls.flush++; )
215	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);
216	if( ret < 0 ) {
217	switch((int)errno) {
218	case EAGAIN:
219	case EINTR:
220	case EBUSY:
221	// Update statistics
222	__STATS__( false, io.calls.errors.busy ++; )
223	return false;
224	default:
225	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
226	}
227	}
228
229	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring %d\n", ret, ctx.fd);
230	__STATS__( true, io.calls.submitted += ret; )
231	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
232	/* paranoid */ verify( ctx.sq.to_submit >= ret );
233
234	ctx.sq.to_submit -= ret;
235
236	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
237
238	// Release the consumed SQEs
239	__release_sqes( ctx );
240
241	/* paranoid */ verify( ! __preemption_enabled() );
242
243	__atomic_store_n(&ctx.proc->io.pending, false, __ATOMIC_RELAXED);
244	}
245
246	ready_schedule_lock();
247	bool ret = __cfa_io_drain( proc );
248	ready_schedule_unlock();
249	return ret;
250	}
251
252	//=============================================================================================
253	// I/O Submissions
254	//=============================================================================================
255
256	// Submition steps :
257	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
258	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
259	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
260	// need to write an allocator that allows allocating concurrently.
261	//
262	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
263	//
264	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
265	// needs to arrive to two concensus at the same time:
266	// A - The order in which entries are listed in the array: no two threads must pick the
267	// same index for their entries
268	// B - When can the tail be update for the kernel. EVERY entries in the array between
269	// head and tail must be fully filled and shouldn't ever be touched again.
270	//
271	//=============================================================================================
272	// Allocation
273	// for user's convenience fill the sqes from the indexes
274	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
275	struct io_uring_sqe * sqes = ctx->sq.sqes;
276	for(i; want) {
277	__cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
278	out_sqes[i] = &sqes[idxs[i]];
279	}
280	}
281
282	// Try to directly allocate from the a given context
283	// Not thread-safe
284	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
285	__sub_ring_t & sq = ctx->sq;
286	const __u32 mask = *sq.mask;
287	__u32 fhead = sq.free_ring.head; // get the current head of the queue
288	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
289
290	// If we don't have enough sqes, fail
291	if((ftail - fhead) < want) { return false; }
292
293	// copy all the indexes we want from the available list
294	for(i; want) {
295	__cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
296	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
297	}
298
299	// Advance the head to mark the indexes as consumed
300	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
301
302	// return success
303	return true;
304	}
305
306	// Allocate an submit queue entry.
307	// The kernel cannot see these entries until they are submitted, but other threads must be
308	// able to see which entries can be used and which are already un used by an other thread
309	// for convenience, return both the index and the pointer to the sqe
310	// sqe == &sqes[idx]
311	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) {
312	__cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
313
314	disable_interrupts();
315	processor * proc = __cfaabi_tls.this_processor;
316	$io_context * ctx = proc->io.ctx;
317	/* paranoid */ verify( __cfaabi_tls.this_processor );
318	/* paranoid */ verify( ctx );
319
320	__cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
321
322	// We can proceed to the fast path
323	if( __alloc(ctx, idxs, want) ) {
324	// Allocation was successful
325	__STATS__( true, io.alloc.fast += 1; )
326	enable_interrupts();
327
328	__cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
329
330	__fill( sqes, want, idxs, ctx );
331	return ctx;
332	}
333	// The fast path failed, fallback
334	__STATS__( true, io.alloc.fail += 1; )
335
336	// Fast path failed, fallback on arbitration
337	__STATS__( true, io.alloc.slow += 1; )
338	enable_interrupts();
339
340	$io_arbiter * ioarb = proc->cltr->io.arbiter;
341	/* paranoid */ verify( ioarb );
342
343	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
344
345	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
346
347	__cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
348
349	__fill( sqes, want, idxs,ret );
350	return ret;
351	}
352
353	//=============================================================================================
354	// submission
355	static inline void __submit_only( struct $io_context * ctx, __u32 idxs[], __u32 have) {
356	// We can proceed to the fast path
357	// Get the right objects
358	__sub_ring_t & sq = ctx->sq;
359	const __u32 mask = *sq.mask;
360	__u32 tail = *sq.kring.tail;
361
362	// Add the sqes to the array
363	for( i; have ) {
364	__cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
365	sq.kring.array[ (tail + i) & mask ] = idxs[i];
366	}
367
368	// Make the sqes visible to the submitter
369	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
370	sq.to_submit += have;
371
372	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_RELAXED);
373	__atomic_store_n(&ctx->proc->io.dirty , true, __ATOMIC_RELAXED);
374	}
375
376	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
377	__sub_ring_t & sq = ctx->sq;
378	__submit_only(ctx, idxs, have);
379
380	if(sq.to_submit > 30) {
381	__tls_stats()->io.flush.full++;
382	__cfa_io_flush( ctx->proc, 0 );
383	}
384	if(!lazy) {
385	__tls_stats()->io.flush.eager++;
386	__cfa_io_flush( ctx->proc, 0 );
387	}
388	}
389
390	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) {
391	__cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
392
393	disable_interrupts();
394	processor * proc = __cfaabi_tls.this_processor;
395	$io_context * ctx = proc->io.ctx;
396	/* paranoid */ verify( __cfaabi_tls.this_processor );
397	/* paranoid */ verify( ctx );
398
399	// Can we proceed to the fast path
400	if( ctx == inctx ) // We have the right instance?
401	{
402	__submit(ctx, idxs, have, lazy);
403
404	// Mark the instance as no longer in-use, re-enable interrupts and return
405	__STATS__( true, io.submit.fast += 1; )
406	enable_interrupts();
407
408	__cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
409	return;
410	}
411
412	// Fast path failed, fallback on arbitration
413	__STATS__( true, io.submit.slow += 1; )
414	enable_interrupts();
415
416	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
417
418	__ioarbiter_submit(inctx, idxs, have, lazy);
419	}
420
421	//=============================================================================================
422	// Flushing
423	// Go through the ring's submit queue and release everything that has already been consumed
424	// by io_uring
425	// This cannot be done by multiple threads
426	static __u32 __release_sqes( struct $io_context & ctx ) {
427	const __u32 mask = *ctx.sq.mask;
428
429	__attribute__((unused))
430	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
431	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
432	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
433
434	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
435
436	// the 3 fields are organized like this diagram
437	// except it's are ring
438	// ---+--------+--------+----
439	// ---+--------+--------+----
440	// ^ ^ ^
441	// phead chead ctail
442
443	// make sure ctail doesn't wrap around and reach phead
444	/* paranoid */ verify(
445	(ctail >= chead && chead >= phead)
446	\|\| (chead >= phead && phead >= ctail)
447	\|\| (phead >= ctail && ctail >= chead)
448	);
449
450	// find the range we need to clear
451	__u32 count = chead - phead;
452
453	if(count == 0) {
454	return 0;
455	}
456
457	// We acquired an previous-head/current-head range
458	// go through the range and release the sqes
459	for( i; count ) {
460	__cfadbg_print_safe(io, "Kernel I/O : release loop\n");
461	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
462	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
463	}
464
465	ctx.sq.kring.released = chead; // note up to were we processed
466	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
467
468	__ioarbiter_notify(ctx);
469
470	return count;
471	}
472
473	//=============================================================================================
474	// I/O Arbiter
475	//=============================================================================================
476	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
477	bool was_empty;
478
479	// Lock the list, it's not thread safe
480	lock( queue.lock __cfaabi_dbg_ctx2 );
481	{
482	was_empty = empty(queue.queue);
483
484	// Add our request to the list
485	add( queue.queue, item );
486
487	// Mark as pending
488	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
489	}
490	unlock( queue.lock );
491
492	return was_empty;
493	}
494
495	static inline bool empty(__outstanding_io_queue & queue ) {
496	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
497	}
498
499	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
500	__cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
501
502	__STATS__( false, io.alloc.block += 1; )
503
504	// No one has any resources left, wait for something to finish
505	// We need to add ourself to a list of pending allocs and wait for an answer
506	__pending_alloc pa;
507	pa.idxs = idxs;
508	pa.want = want;
509
510	enqueue(this.pending, (__outstanding_io&)pa);
511
512	wait( pa.sem );
513
514	return pa.ctx;
515
516	}
517
518	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
519	/* paranoid */ verify( !empty(this.pending.queue) );
520
521	lock( this.pending.lock __cfaabi_dbg_ctx2 );
522	{
523	while( !empty(this.pending.queue) ) {
524	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
525	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
526	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
527
528	if( have > pa.want ) goto DONE;
529	drop( this.pending.queue );
530
531	/* paranoid */__attribute__((unused)) bool ret =
532
533	__alloc(ctx, pa.idxs, pa.want);
534
535	/* paranoid */ verify( ret );
536
537	pa.ctx = ctx;
538
539	post( pa.sem );
540	}
541
542	this.pending.empty = true;
543	DONE:;
544	}
545	unlock( this.pending.lock );
546	}
547
548	static void __ioarbiter_notify( $io_context & ctx ) {
549	if(!empty( ctx.arbiter->pending )) {
550	__ioarbiter_notify( *ctx.arbiter, &ctx );
551	}
552	}
553
554	// Simply append to the pending
555	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
556	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
557
558	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
559
560	__external_io ei;
561	ei.idxs = idxs;
562	ei.have = have;
563	ei.lazy = lazy;
564
565	bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
566
567	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_SEQ_CST);
568
569	if( we ) {
570	sigval_t value = { PREEMPT_IO };
571	pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
572	}
573
574	wait( ei.sem );
575
576	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
577	}
578
579	static void __ioarbiter_flush( $io_context & ctx ) {
580	if(!empty( ctx.ext_sq )) {
581	__STATS__( false, io.flush.external += 1; )
582
583	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
584
585	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
586	{
587	while( !empty(ctx.ext_sq.queue) ) {
588	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
589
590	__submit_only(&ctx, ei.idxs, ei.have);
591
592	post( ei.sem );
593	}
594
595	ctx.ext_sq.empty = true;
596	}
597	unlock(ctx.ext_sq.lock );
598	}
599	}
600
601	#if defined(CFA_WITH_IO_URING_IDLE)
602	bool __kernel_read(processor * proc, io_future_t & future, iovec & iov, int fd) {
603	$io_context * ctx = proc->io.ctx;
604	/* paranoid */ verify( ! __preemption_enabled() );
605	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
606	/* paranoid */ verify( ctx );
607
608	__u32 idx;
609	struct io_uring_sqe * sqe;
610
611	// We can proceed to the fast path
612	if( !__alloc(ctx, &idx, 1) ) return false;
613
614	// Allocation was successful
615	__fill( &sqe, 1, &idx, ctx );
616
617	sqe->user_data = (uintptr_t)&future;
618	sqe->flags = 0;
619	sqe->fd = fd;
620	sqe->off = 0;
621	sqe->ioprio = 0;
622	sqe->fsync_flags = 0;
623	sqe->__pad2[0] = 0;
624	sqe->__pad2[1] = 0;
625	sqe->__pad2[2] = 0;
626
627	#if defined(CFA_HAVE_IORING_OP_READ)
628	sqe->opcode = IORING_OP_READ;
629	sqe->addr = (uint64_t)iov.iov_base;
630	sqe->len = iov.iov_len;
631	#elif defined(CFA_HAVE_READV) && defined(CFA_HAVE_IORING_OP_READV)
632	sqe->opcode = IORING_OP_READV;
633	sqe->addr = (uintptr_t)&iov;
634	sqe->len = 1;
635	#else
636	#error CFA_WITH_IO_URING_IDLE but none of CFA_HAVE_READV, CFA_HAVE_IORING_OP_READV or CFA_HAVE_IORING_OP_READ defined
637	#endif
638
639	asm volatile("": : :"memory");
640
641	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
642	__submit( ctx, &idx, 1, true );
643
644	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
645	/* paranoid */ verify( ! __preemption_enabled() );
646
647	return true;
648	}
649	#endif
650	#endif

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