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ADT ast-experimental enum pthread-emulation qualifiedEnum

Last change on this file since 8631c84 was 3caf5e3, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
Re-read cq information after acquire. Hoping this is the cause for the build failure
Property mode set to `100644`
File size: 19.7 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	return false;
114	}
115
116	unsigned long long ts_prev = ctx->cq.ts;
117
118	// re-read the head and tail in case it already changed.
119	const __u32 head = *ctx->cq.head;
120	const __u32 tail = *ctx->cq.tail;
121	const __u32 count = tail - head;
122	__STATS__( false, io.calls.drain++; io.calls.completed += count; )
123
124	for(i; count) {
125	unsigned idx = (head + i) & mask;
126	volatile struct io_uring_cqe & cqe = ctx->cq.cqes[idx];
127
128	/* paranoid */ verify(&cqe);
129
130	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
131	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
132
133	__kernel_unpark( fulfil( *future, cqe.res, false ), UNPARK_LOCAL );
134	}
135
136	__cfadbg_print_safe(io, "Kernel I/O : %u completed\n", count);
137	unsigned long long ts_next = ctx->cq.ts = rdtscl();
138
139	// Mark to the kernel that the cqe has been seen
140	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
141	__atomic_store_n( ctx->cq.head, head + count, __ATOMIC_SEQ_CST );
142
143	/* paranoid */ verify( ready_schedule_islocked() );
144	/* paranoid */ verify( ! __preemption_enabled() );
145
146	__atomic_unlock(&ctx->cq.lock);
147
148	touch_tsc( cltr->sched.io.tscs, ctx->cq.id, ts_prev, ts_next );
149
150	return true;
151	}
152
153	bool __cfa_io_drain( processor * proc ) {
154	bool local = false;
155	bool remote = false;
156
157	cluster * const cltr = proc->cltr;
158	$io_context * const ctx = proc->io.ctx;
159	/* paranoid */ verify( cltr );
160	/* paranoid */ verify( ctx );
161
162	with(cltr->sched) {
163	const size_t ctxs_count = io.count;
164
165	/* paranoid */ verify( ready_schedule_islocked() );
166	/* paranoid */ verify( ! __preemption_enabled() );
167	/* paranoid */ verify( active_processor() == proc );
168	/* paranoid */ verify( __shard_factor.io > 0 );
169	/* paranoid */ verify( ctxs_count > 0 );
170	/* paranoid */ verify( ctx->cq.id < ctxs_count );
171
172	const unsigned this_cache = cache_id(cltr, ctx->cq.id / __shard_factor.io);
173	const unsigned long long ctsc = rdtscl();
174
175	if(proc->io.target == MAX) {
176	uint64_t chaos = __tls_rand();
177	unsigned ext = chaos & 0xff;
178	unsigned other = (chaos >> 8) % (ctxs_count);
179
180	if(ext < 3 \|\| __atomic_load_n(&caches[other / __shard_factor.io].id, __ATOMIC_RELAXED) == this_cache) {
181	proc->io.target = other;
182	}
183	}
184	else {
185	const unsigned target = proc->io.target;
186	/* paranoid */ verify( io.tscs[target].tv != MAX );
187	if(target < ctxs_count) {
188	const unsigned long long cutoff = calc_cutoff(ctsc, ctx->cq.id, ctxs_count, io.data, io.tscs, __shard_factor.io);
189	const unsigned long long age = moving_average(ctsc, io.tscs[target].tv, io.tscs[target].ma);
190	// __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");
191	if(age > cutoff) {
192	remote = __cfa_do_drain( io.data[target], cltr );
193	}
194	}
195	proc->io.target = MAX;
196	}
197	}
198
199
200	// Drain the local queue
201	local = __cfa_do_drain( proc->io.ctx, cltr );
202
203	/* paranoid */ verify( ready_schedule_islocked() );
204	/* paranoid */ verify( ! __preemption_enabled() );
205	/* paranoid */ verify( active_processor() == proc );
206	return local \|\| remote;
207	}
208
209	bool __cfa_io_flush( processor * proc, int min_comp ) {
210	/* paranoid */ verify( ! __preemption_enabled() );
211	/* paranoid */ verify( proc );
212	/* paranoid */ verify( proc->io.ctx );
213
214	cluster * cltr = proc->cltr;
215	$io_context & ctx = *proc->io.ctx;
216
217	__ioarbiter_flush( ctx );
218
219	if(ctx.sq.to_submit != 0 \|\| min_comp > 0) {
220
221	__STATS__( true, io.calls.flush++; )
222	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);
223	if( ret < 0 ) {
224	switch((int)errno) {
225	case EAGAIN:
226	case EINTR:
227	case EBUSY:
228	// Update statistics
229	__STATS__( false, io.calls.errors.busy ++; )
230	return false;
231	default:
232	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
233	}
234	}
235
236	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring %d\n", ret, ctx.fd);
237	__STATS__( true, io.calls.submitted += ret; )
238	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
239	/* paranoid */ verify( ctx.sq.to_submit >= ret );
240
241	ctx.sq.to_submit -= ret;
242
243	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
244
245	// Release the consumed SQEs
246	__release_sqes( ctx );
247
248	/* paranoid */ verify( ! __preemption_enabled() );
249
250	__atomic_store_n(&ctx.proc->io.pending, false, __ATOMIC_RELAXED);
251	}
252
253	ready_schedule_lock();
254	bool ret = __cfa_io_drain( proc );
255	ready_schedule_unlock();
256	return ret;
257	}
258
259	//=============================================================================================
260	// I/O Submissions
261	//=============================================================================================
262
263	// Submition steps :
264	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
265	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
266	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
267	// need to write an allocator that allows allocating concurrently.
268	//
269	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
270	//
271	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
272	// needs to arrive to two concensus at the same time:
273	// A - The order in which entries are listed in the array: no two threads must pick the
274	// same index for their entries
275	// B - When can the tail be update for the kernel. EVERY entries in the array between
276	// head and tail must be fully filled and shouldn't ever be touched again.
277	//
278	//=============================================================================================
279	// Allocation
280	// for user's convenience fill the sqes from the indexes
281	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
282	struct io_uring_sqe * sqes = ctx->sq.sqes;
283	for(i; want) {
284	__cfadbg_print_safe(io, "Kernel I/O : filling loop\n");
285	out_sqes[i] = &sqes[idxs[i]];
286	}
287	}
288
289	// Try to directly allocate from the a given context
290	// Not thread-safe
291	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
292	__sub_ring_t & sq = ctx->sq;
293	const __u32 mask = *sq.mask;
294	__u32 fhead = sq.free_ring.head; // get the current head of the queue
295	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
296
297	// If we don't have enough sqes, fail
298	if((ftail - fhead) < want) { return false; }
299
300	// copy all the indexes we want from the available list
301	for(i; want) {
302	__cfadbg_print_safe(io, "Kernel I/O : allocating loop\n");
303	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
304	}
305
306	// Advance the head to mark the indexes as consumed
307	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
308
309	// return success
310	return true;
311	}
312
313	// Allocate an submit queue entry.
314	// The kernel cannot see these entries until they are submitted, but other threads must be
315	// able to see which entries can be used and which are already un used by an other thread
316	// for convenience, return both the index and the pointer to the sqe
317	// sqe == &sqes[idx]
318	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) {
319	__cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
320
321	disable_interrupts();
322	processor * proc = __cfaabi_tls.this_processor;
323	$io_context * ctx = proc->io.ctx;
324	/* paranoid */ verify( __cfaabi_tls.this_processor );
325	/* paranoid */ verify( ctx );
326
327	__cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
328
329	// We can proceed to the fast path
330	if( __alloc(ctx, idxs, want) ) {
331	// Allocation was successful
332	__STATS__( true, io.alloc.fast += 1; )
333	enable_interrupts();
334
335	__cfadbg_print_safe(io, "Kernel I/O : fast allocation successful from ring %d\n", ctx->fd);
336
337	__fill( sqes, want, idxs, ctx );
338	return ctx;
339	}
340	// The fast path failed, fallback
341	__STATS__( true, io.alloc.fail += 1; )
342
343	// Fast path failed, fallback on arbitration
344	__STATS__( true, io.alloc.slow += 1; )
345	enable_interrupts();
346
347	$io_arbiter * ioarb = proc->cltr->io.arbiter;
348	/* paranoid */ verify( ioarb );
349
350	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
351
352	struct $io_context * ret = __ioarbiter_allocate(*ioarb, idxs, want);
353
354	__cfadbg_print_safe(io, "Kernel I/O : slow allocation completed from ring %d\n", ret->fd);
355
356	__fill( sqes, want, idxs,ret );
357	return ret;
358	}
359
360	//=============================================================================================
361	// submission
362	static inline void __submit_only( struct $io_context * ctx, __u32 idxs[], __u32 have) {
363	// We can proceed to the fast path
364	// Get the right objects
365	__sub_ring_t & sq = ctx->sq;
366	const __u32 mask = *sq.mask;
367	__u32 tail = *sq.kring.tail;
368
369	// Add the sqes to the array
370	for( i; have ) {
371	__cfadbg_print_safe(io, "Kernel I/O : __submit loop\n");
372	sq.kring.array[ (tail + i) & mask ] = idxs[i];
373	}
374
375	// Make the sqes visible to the submitter
376	__atomic_store_n(sq.kring.tail, tail + have, __ATOMIC_RELEASE);
377	sq.to_submit += have;
378
379	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_RELAXED);
380	__atomic_store_n(&ctx->proc->io.dirty , true, __ATOMIC_RELAXED);
381	}
382
383	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have, bool lazy) {
384	__sub_ring_t & sq = ctx->sq;
385	__submit_only(ctx, idxs, have);
386
387	if(sq.to_submit > 30) {
388	__tls_stats()->io.flush.full++;
389	__cfa_io_flush( ctx->proc, 0 );
390	}
391	if(!lazy) {
392	__tls_stats()->io.flush.eager++;
393	__cfa_io_flush( ctx->proc, 0 );
394	}
395	}
396
397	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have, bool lazy ) __attribute__((nonnull (1))) {
398	__cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u (%s)\n", have, lazy ? "lazy" : "eager");
399
400	disable_interrupts();
401	processor * proc = __cfaabi_tls.this_processor;
402	$io_context * ctx = proc->io.ctx;
403	/* paranoid */ verify( __cfaabi_tls.this_processor );
404	/* paranoid */ verify( ctx );
405
406	// Can we proceed to the fast path
407	if( ctx == inctx ) // We have the right instance?
408	{
409	__submit(ctx, idxs, have, lazy);
410
411	// Mark the instance as no longer in-use, re-enable interrupts and return
412	__STATS__( true, io.submit.fast += 1; )
413	enable_interrupts();
414
415	__cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
416	return;
417	}
418
419	// Fast path failed, fallback on arbitration
420	__STATS__( true, io.submit.slow += 1; )
421	enable_interrupts();
422
423	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
424
425	__ioarbiter_submit(inctx, idxs, have, lazy);
426	}
427
428	//=============================================================================================
429	// Flushing
430	// Go through the ring's submit queue and release everything that has already been consumed
431	// by io_uring
432	// This cannot be done by multiple threads
433	static __u32 __release_sqes( struct $io_context & ctx ) {
434	const __u32 mask = *ctx.sq.mask;
435
436	__attribute__((unused))
437	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
438	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
439	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
440
441	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
442
443	// the 3 fields are organized like this diagram
444	// except it's are ring
445	// ---+--------+--------+----
446	// ---+--------+--------+----
447	// ^ ^ ^
448	// phead chead ctail
449
450	// make sure ctail doesn't wrap around and reach phead
451	/* paranoid */ verify(
452	(ctail >= chead && chead >= phead)
453	\|\| (chead >= phead && phead >= ctail)
454	\|\| (phead >= ctail && ctail >= chead)
455	);
456
457	// find the range we need to clear
458	__u32 count = chead - phead;
459
460	if(count == 0) {
461	return 0;
462	}
463
464	// We acquired an previous-head/current-head range
465	// go through the range and release the sqes
466	for( i; count ) {
467	__cfadbg_print_safe(io, "Kernel I/O : release loop\n");
468	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
469	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
470	}
471
472	ctx.sq.kring.released = chead; // note up to were we processed
473	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
474
475	__ioarbiter_notify(ctx);
476
477	return count;
478	}
479
480	//=============================================================================================
481	// I/O Arbiter
482	//=============================================================================================
483	static inline bool enqueue(__outstanding_io_queue & queue, __outstanding_io & item) {
484	bool was_empty;
485
486	// Lock the list, it's not thread safe
487	lock( queue.lock __cfaabi_dbg_ctx2 );
488	{
489	was_empty = empty(queue.queue);
490
491	// Add our request to the list
492	add( queue.queue, item );
493
494	// Mark as pending
495	__atomic_store_n( &queue.empty, false, __ATOMIC_SEQ_CST );
496	}
497	unlock( queue.lock );
498
499	return was_empty;
500	}
501
502	static inline bool empty(__outstanding_io_queue & queue ) {
503	return __atomic_load_n( &queue.empty, __ATOMIC_SEQ_CST);
504	}
505
506	static $io_context * __ioarbiter_allocate( $io_arbiter & this, __u32 idxs[], __u32 want ) {
507	__cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
508
509	__STATS__( false, io.alloc.block += 1; )
510
511	// No one has any resources left, wait for something to finish
512	// We need to add ourself to a list of pending allocs and wait for an answer
513	__pending_alloc pa;
514	pa.idxs = idxs;
515	pa.want = want;
516
517	enqueue(this.pending, (__outstanding_io&)pa);
518
519	wait( pa.sem );
520
521	return pa.ctx;
522
523	}
524
525	static void __ioarbiter_notify( $io_arbiter & this, $io_context * ctx ) {
526	/* paranoid */ verify( !empty(this.pending.queue) );
527
528	lock( this.pending.lock __cfaabi_dbg_ctx2 );
529	{
530	while( !empty(this.pending.queue) ) {
531	__cfadbg_print_safe(io, "Kernel I/O : notifying\n");
532	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
533	__pending_alloc & pa = (__pending_alloc&)head( this.pending.queue );
534
535	if( have > pa.want ) goto DONE;
536	drop( this.pending.queue );
537
538	/* paranoid */__attribute__((unused)) bool ret =
539
540	__alloc(ctx, pa.idxs, pa.want);
541
542	/* paranoid */ verify( ret );
543
544	pa.ctx = ctx;
545
546	post( pa.sem );
547	}
548
549	this.pending.empty = true;
550	DONE:;
551	}
552	unlock( this.pending.lock );
553	}
554
555	static void __ioarbiter_notify( $io_context & ctx ) {
556	if(!empty( ctx.arbiter->pending )) {
557	__ioarbiter_notify( *ctx.arbiter, &ctx );
558	}
559	}
560
561	// Simply append to the pending
562	static void __ioarbiter_submit( $io_context * ctx, __u32 idxs[], __u32 have, bool lazy ) {
563	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
564
565	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
566
567	__external_io ei;
568	ei.idxs = idxs;
569	ei.have = have;
570	ei.lazy = lazy;
571
572	bool we = enqueue(ctx->ext_sq, (__outstanding_io&)ei);
573
574	__atomic_store_n(&ctx->proc->io.pending, true, __ATOMIC_SEQ_CST);
575
576	if( we ) {
577	sigval_t value = { PREEMPT_IO };
578	pthread_sigqueue(ctx->proc->kernel_thread, SIGUSR1, value);
579	}
580
581	wait( ei.sem );
582
583	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
584	}
585
586	static void __ioarbiter_flush( $io_context & ctx ) {
587	if(!empty( ctx.ext_sq )) {
588	__STATS__( false, io.flush.external += 1; )
589
590	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
591
592	lock( ctx.ext_sq.lock __cfaabi_dbg_ctx2 );
593	{
594	while( !empty(ctx.ext_sq.queue) ) {
595	__external_io & ei = (__external_io&)drop( ctx.ext_sq.queue );
596
597	__submit_only(&ctx, ei.idxs, ei.have);
598
599	post( ei.sem );
600	}
601
602	ctx.ext_sq.empty = true;
603	}
604	unlock(ctx.ext_sq.lock );
605	}
606	}
607
608	#if defined(CFA_WITH_IO_URING_IDLE)
609	bool __kernel_read(processor * proc, io_future_t & future, iovec & iov, int fd) {
610	$io_context * ctx = proc->io.ctx;
611	/* paranoid */ verify( ! __preemption_enabled() );
612	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
613	/* paranoid */ verify( ctx );
614
615	__u32 idx;
616	struct io_uring_sqe * sqe;
617
618	// We can proceed to the fast path
619	if( !__alloc(ctx, &idx, 1) ) return false;
620
621	// Allocation was successful
622	__fill( &sqe, 1, &idx, ctx );
623
624	sqe->user_data = (uintptr_t)&future;
625	sqe->flags = 0;
626	sqe->fd = fd;
627	sqe->off = 0;
628	sqe->ioprio = 0;
629	sqe->fsync_flags = 0;
630	sqe->__pad2[0] = 0;
631	sqe->__pad2[1] = 0;
632	sqe->__pad2[2] = 0;
633
634	#if defined(CFA_HAVE_IORING_OP_READ)
635	sqe->opcode = IORING_OP_READ;
636	sqe->addr = (uint64_t)iov.iov_base;
637	sqe->len = iov.iov_len;
638	#elif defined(CFA_HAVE_READV) && defined(CFA_HAVE_IORING_OP_READV)
639	sqe->opcode = IORING_OP_READV;
640	sqe->addr = (uintptr_t)&iov;
641	sqe->len = 1;
642	#else
643	#error CFA_WITH_IO_URING_IDLE but none of CFA_HAVE_READV, CFA_HAVE_IORING_OP_READV or CFA_HAVE_IORING_OP_READ defined
644	#endif
645
646	asm volatile("": : :"memory");
647
648	/* paranoid */ verify( sqe->user_data == (uintptr_t)&future );
649	__submit( ctx, &idx, 1, true );
650
651	/* paranoid */ verify( proc == __cfaabi_tls.this_processor );
652	/* paranoid */ verify( ! __preemption_enabled() );
653
654	return true;
655	}
656	#endif
657	#endif

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