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io.cfa @ 95b3a9c

ADTarm-ehast-experimentalenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-exprpthread-emulationqualifiedEnum

Last change on this file since 95b3a9c was 2fab24e3, checked in by Thierry Delisle <tdelisle@…>, 3 years ago
Fixed some warnings and printing.
Property mode set to `100644`
File size: 21.4 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
18	#if defined(__CFA_DEBUG__)
19	// #define __CFA_DEBUG_PRINT_IO__
20	// #define __CFA_DEBUG_PRINT_IO_CORE__
21	#endif
22
23
24	#if defined(CFA_HAVE_LINUX_IO_URING_H)
25	#define _GNU_SOURCE /* See feature_test_macros(7) */
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
35	#include <linux/io_uring.h>
36	}
37
38	#include "stats.hfa"
39	#include "kernel.hfa"
40	#include "kernel/fwd.hfa"
41	#include "io/types.hfa"
42
43	__attribute__((unused)) static const char * opcodes[] = {
44	"OP_NOP",
45	"OP_READV",
46	"OP_WRITEV",
47	"OP_FSYNC",
48	"OP_READ_FIXED",
49	"OP_WRITE_FIXED",
50	"OP_POLL_ADD",
51	"OP_POLL_REMOVE",
52	"OP_SYNC_FILE_RANGE",
53	"OP_SENDMSG",
54	"OP_RECVMSG",
55	"OP_TIMEOUT",
56	"OP_TIMEOUT_REMOVE",
57	"OP_ACCEPT",
58	"OP_ASYNC_CANCEL",
59	"OP_LINK_TIMEOUT",
60	"OP_CONNECT",
61	"OP_FALLOCATE",
62	"OP_OPENAT",
63	"OP_CLOSE",
64	"OP_FILES_UPDATE",
65	"OP_STATX",
66	"OP_READ",
67	"OP_WRITE",
68	"OP_FADVISE",
69	"OP_MADVISE",
70	"OP_SEND",
71	"OP_RECV",
72	"OP_OPENAT2",
73	"OP_EPOLL_CTL",
74	"OP_SPLICE",
75	"OP_PROVIDE_BUFFERS",
76	"OP_REMOVE_BUFFERS",
77	"OP_TEE",
78	"INVALID_OP"
79	};
80
81	// returns true of acquired as leader or second leader
82	static inline bool try_lock( __leaderlock_t & this ) {
83	const uintptr_t thrd = 1z \| (uintptr_t)active_thread();
84	bool block;
85	disable_interrupts();
86	for() {
87	struct $thread * expected = this.value;
88	if( 1p != expected && 0p != expected ) {
89	/* paranoid */ verify( thrd != (uintptr_t)expected ); // We better not already be the next leader
90	enable_interrupts( __cfaabi_dbg_ctx );
91	return false;
92	}
93	struct $thread * desired;
94	if( 0p == expected ) {
95	// If the lock isn't locked acquire it, no need to block
96	desired = 1p;
97	block = false;
98	}
99	else {
100	// If the lock is already locked try becomming the next leader
101	desired = (struct $thread *)thrd;
102	block = true;
103	}
104	if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
105	}
106	if( block ) {
107	enable_interrupts( __cfaabi_dbg_ctx );
108	park();
109	disable_interrupts();
110	}
111	return true;
112	}
113
114	static inline bool next( __leaderlock_t & this ) {
115	/* paranoid */ verify( ! __preemption_enabled() );
116	struct $thread * nextt;
117	for() {
118	struct $thread * expected = this.value;
119	/* paranoid */ verify( (1 & (uintptr_t)expected) == 1 ); // The lock better be locked
120
121	struct $thread * desired;
122	if( 1p == expected ) {
123	// No next leader, just unlock
124	desired = 0p;
125	nextt = 0p;
126	}
127	else {
128	// There is a next leader, remove but keep locked
129	desired = 1p;
130	nextt = (struct $thread *)(~1z & (uintptr_t)expected);
131	}
132	if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
133	}
134
135	if(nextt) {
136	unpark( nextt );
137	enable_interrupts( __cfaabi_dbg_ctx );
138	return true;
139	}
140	enable_interrupts( __cfaabi_dbg_ctx );
141	return false;
142	}
143
144	//=============================================================================================
145	// I/O Syscall
146	//=============================================================================================
147	static int __io_uring_enter( struct __io_data & ring, unsigned to_submit, bool get ) {
148	bool need_sys_to_submit = false;
149	bool need_sys_to_complete = false;
150	unsigned flags = 0;
151
152	TO_SUBMIT:
153	if( to_submit > 0 ) {
154	if( !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
155	need_sys_to_submit = true;
156	break TO_SUBMIT;
157	}
158	if( (*ring.submit_q.flags) & IORING_SQ_NEED_WAKEUP ) {
159	need_sys_to_submit = true;
160	flags \|= IORING_ENTER_SQ_WAKEUP;
161	}
162	}
163
164	if( get && !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
165	flags \|= IORING_ENTER_GETEVENTS;
166	if( (ring.ring_flags & IORING_SETUP_IOPOLL) ) {
167	need_sys_to_complete = true;
168	}
169	}
170
171	int ret = 0;
172	if( need_sys_to_submit \|\| need_sys_to_complete ) {
173	__cfadbg_print_safe(io_core, "Kernel I/O : IO_URING enter %d %u %u\n", ring.fd, to_submit, flags);
174	ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, 0, flags, (sigset_t *)0p, _NSIG / 8);
175	__cfadbg_print_safe(io_core, "Kernel I/O : IO_URING %d returned %d\n", ring.fd, ret);
176
177	if( ret < 0 ) {
178	switch((int)errno) {
179	case EAGAIN:
180	case EINTR:
181	case EBUSY:
182	ret = -1;
183	break;
184	default:
185	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
186	}
187	}
188	}
189
190	// Memory barrier
191	__atomic_thread_fence( __ATOMIC_SEQ_CST );
192	return ret;
193	}
194
195	//=============================================================================================
196	// I/O Polling
197	//=============================================================================================
198	static unsigned __collect_submitions( struct __io_data & ring );
199	static __u32 __release_consumed_submission( struct __io_data & ring );
200	static inline void __clean( volatile struct io_uring_sqe * sqe );
201
202	// Process a single completion message from the io_uring
203	// This is NOT thread-safe
204	static inline void process( volatile struct io_uring_cqe & cqe ) {
205	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
206	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
207
208	fulfil( *future, cqe.res );
209	}
210
211	static [int, bool] __drain_io( & struct __io_data ring ) {
212	/* paranoid */ verify( ! __preemption_enabled() );
213
214	unsigned to_submit = 0;
215	if( ring.poller_submits ) {
216	// If the poller thread also submits, then we need to aggregate the submissions which are ready
217	to_submit = __collect_submitions( ring );
218	}
219
220	int ret = __io_uring_enter(ring, to_submit, true);
221	if( ret < 0 ) {
222	return [0, true];
223	}
224
225	// update statistics
226	if (to_submit > 0) {
227	__STATS__( true,
228	if( to_submit > 0 ) {
229	io.submit_q.submit_avg.rdy += to_submit;
230	io.submit_q.submit_avg.csm += ret;
231	io.submit_q.submit_avg.cnt += 1;
232	}
233	)
234	}
235
236	__atomic_thread_fence( __ATOMIC_SEQ_CST );
237
238	// Release the consumed SQEs
239	__release_consumed_submission( ring );
240
241	// Drain the queue
242	unsigned head = *ring.completion_q.head;
243	unsigned tail = *ring.completion_q.tail;
244	const __u32 mask = *ring.completion_q.mask;
245
246	// Nothing was new return 0
247	if (head == tail) {
248	return [0, to_submit > 0];
249	}
250
251	__u32 count = tail - head;
252	/* paranoid */ verify( count != 0 );
253	for(i; count) {
254	unsigned idx = (head + i) & mask;
255	volatile struct io_uring_cqe & cqe = ring.completion_q.cqes[idx];
256
257	/* paranoid */ verify(&cqe);
258
259	process( cqe );
260	}
261
262	// Mark to the kernel that the cqe has been seen
263	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
264	__atomic_fetch_add( ring.completion_q.head, count, __ATOMIC_SEQ_CST );
265
266	return [count, count > 0 \|\| to_submit > 0];
267	}
268
269	void main( $io_ctx_thread & this ) {
270	__ioctx_register( this );
271
272	__cfadbg_print_safe(io_core, "Kernel I/O : IO poller %d (%p) ready\n", this.ring->fd, &this);
273
274	const int reset_cnt = 5;
275	int reset = reset_cnt;
276	// Then loop until we need to start
277	LOOP:
278	while(!__atomic_load_n(&this.done, __ATOMIC_SEQ_CST)) {
279	// Drain the io
280	int count;
281	bool again;
282	disable_interrupts();
283	[count, again] = __drain_io( *this.ring );
284
285	if(!again) reset--;
286
287	// Update statistics
288	__STATS__( true,
289	io.complete_q.completed_avg.val += count;
290	io.complete_q.completed_avg.cnt += 1;
291	)
292	enable_interrupts( __cfaabi_dbg_ctx );
293
294	// If we got something, just yield and check again
295	if(reset > 1) {
296	yield();
297	continue LOOP;
298	}
299
300	// We alread failed to find completed entries a few time.
301	if(reset == 1) {
302	// Rearm the context so it can block
303	// but don't block right away
304	// we need to retry one last time in case
305	// something completed just now
306	__ioctx_prepare_block( this );
307	continue LOOP;
308	}
309
310	__STATS__( false,
311	io.complete_q.blocks += 1;
312	)
313	__cfadbg_print_safe(io_core, "Kernel I/O : Parking io poller %d (%p)\n", this.ring->fd, &this);
314
315	// block this thread
316	wait( this.sem );
317
318	// restore counter
319	reset = reset_cnt;
320	}
321
322	__cfadbg_print_safe(io_core, "Kernel I/O : Fast poller %d (%p) stopping\n", this.ring->fd, &this);
323
324	__ioctx_unregister( this );
325	}
326
327	//=============================================================================================
328	// I/O Submissions
329	//=============================================================================================
330
331	// Submition steps :
332	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
333	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
334	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
335	// need to write an allocator that allows allocating concurrently.
336	//
337	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
338	//
339	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
340	// needs to arrive to two concensus at the same time:
341	// A - The order in which entries are listed in the array: no two threads must pick the
342	// same index for their entries
343	// B - When can the tail be update for the kernel. EVERY entries in the array between
344	// head and tail must be fully filled and shouldn't ever be touched again.
345	//
346
347	// Allocate an submit queue entry.
348	// The kernel cannot see these entries until they are submitted, but other threads must be
349	// able to see which entries can be used and which are already un used by an other thread
350	// for convenience, return both the index and the pointer to the sqe
351	// sqe == &sqes[idx]
352	[* volatile struct io_uring_sqe, __u32] __submit_alloc( struct __io_data & ring, __u64 data ) {
353	/* paranoid */ verify( data != 0 );
354
355	// Prepare the data we need
356	__attribute((unused)) int len = 0;
357	__attribute((unused)) int block = 0;
358	__u32 cnt = *ring.submit_q.num;
359	__u32 mask = *ring.submit_q.mask;
360
361	__u32 off = thread_rand();
362
363	// Loop around looking for an available spot
364	for() {
365	// Look through the list starting at some offset
366	for(i; cnt) {
367	__u64 expected = 3;
368	__u32 idx = (i + off) & mask; // Get an index from a random
369	volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
370	volatile __u64 * udata = &sqe->user_data;
371
372	// Allocate the entry by CASing the user_data field from 0 to the future address
373	if( *udata == expected &&
374	__atomic_compare_exchange_n( udata, &expected, data, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) )
375	{
376	// update statistics
377	__STATS__( false,
378	io.submit_q.alloc_avg.val += len;
379	io.submit_q.alloc_avg.block += block;
380	io.submit_q.alloc_avg.cnt += 1;
381	)
382
383	// debug log
384	__cfadbg_print_safe( io, "Kernel I/O : allocated [%p, %u] for %p (%p)\n", sqe, idx, active_thread(), (void*)data );
385
386	// Success return the data
387	return [sqe, idx];
388	}
389	verify(expected != data);
390
391	// This one was used
392	len ++;
393	}
394
395	block++;
396
397	yield();
398	}
399	}
400
401	static inline __u32 __submit_to_ready_array( struct __io_data & ring, __u32 idx, const __u32 mask ) {
402	/* paranoid */ verify( idx <= mask );
403	/* paranoid */ verify( idx != -1ul32 );
404
405	// We need to find a spot in the ready array
406	__attribute((unused)) int len = 0;
407	__attribute((unused)) int block = 0;
408	__u32 ready_mask = ring.submit_q.ready_cnt - 1;
409
410	__u32 off = thread_rand();
411
412	__u32 picked;
413	LOOKING: for() {
414	for(i; ring.submit_q.ready_cnt) {
415	picked = (i + off) & ready_mask;
416	__u32 expected = -1ul32;
417	if( __atomic_compare_exchange_n( &ring.submit_q.ready[picked], &expected, idx, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) ) {
418	break LOOKING;
419	}
420	verify(expected != idx);
421
422	len ++;
423	}
424
425	block++;
426
427	__u32 released = __release_consumed_submission( ring );
428	if( released == 0 ) {
429	yield();
430	}
431	}
432
433	// update statistics
434	__STATS__( false,
435	io.submit_q.look_avg.val += len;
436	io.submit_q.look_avg.block += block;
437	io.submit_q.look_avg.cnt += 1;
438	)
439
440	return picked;
441	}
442
443	void __submit( struct io_context * ctx, __u32 idx ) __attribute__((nonnull (1))) {
444	__io_data & ring = *ctx->thrd.ring;
445
446	{
447	__attribute__((unused)) volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
448	__cfadbg_print_safe( io,
449	"Kernel I/O : submitting %u (%p) for %p\n"
450	" data: %p\n"
451	" opcode: %s\n"
452	" fd: %d\n"
453	" flags: %d\n"
454	" prio: %d\n"
455	" off: %p\n"
456	" addr: %p\n"
457	" len: %d\n"
458	" other flags: %d\n"
459	" splice fd: %d\n"
460	" pad[0]: %llu\n"
461	" pad[1]: %llu\n"
462	" pad[2]: %llu\n",
463	idx, sqe,
464	active_thread(),
465	(void*)sqe->user_data,
466	opcodes[sqe->opcode],
467	sqe->fd,
468	sqe->flags,
469	sqe->ioprio,
470	(void*)sqe->off,
471	(void*)sqe->addr,
472	sqe->len,
473	sqe->accept_flags,
474	sqe->splice_fd_in,
475	sqe->__pad2[0],
476	sqe->__pad2[1],
477	sqe->__pad2[2]
478	);
479	}
480
481
482	// Get now the data we definetely need
483	volatile __u32 * const tail = ring.submit_q.tail;
484	const __u32 mask = *ring.submit_q.mask;
485
486	// There are 2 submission schemes, check which one we are using
487	if( ring.poller_submits ) {
488	// If the poller thread submits, then we just need to add this to the ready array
489	__submit_to_ready_array( ring, idx, mask );
490
491	post( ctx->thrd.sem );
492
493	__cfadbg_print_safe( io, "Kernel I/O : Added %u to ready for %p\n", idx, active_thread() );
494	}
495	else if( ring.eager_submits ) {
496	__attribute__((unused)) __u32 picked = __submit_to_ready_array( ring, idx, mask );
497
498	#if defined(LEADER_LOCK)
499	if( !try_lock(ring.submit_q.submit_lock) ) {
500	__STATS__( false,
501	io.submit_q.helped += 1;
502	)
503	return;
504	}
505	/* paranoid */ verify( ! __preemption_enabled() );
506	__STATS__( true,
507	io.submit_q.leader += 1;
508	)
509	#else
510	for() {
511	yield();
512
513	if( try_lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2) ) {
514	__STATS__( false,
515	io.submit_q.leader += 1;
516	)
517	break;
518	}
519
520	// If some one else collected our index, we are done
521	#warning ABA problem
522	if( ring.submit_q.ready[picked] != idx ) {
523	__STATS__( false,
524	io.submit_q.helped += 1;
525	)
526	return;
527	}
528
529	__STATS__( false,
530	io.submit_q.busy += 1;
531	)
532	}
533	#endif
534
535	// We got the lock
536	// Collect the submissions
537	unsigned to_submit = __collect_submitions( ring );
538
539	// Actually submit
540	int ret = __io_uring_enter( ring, to_submit, false );
541
542	#if defined(LEADER_LOCK)
543	/* paranoid */ verify( ! __preemption_enabled() );
544	next(ring.submit_q.submit_lock);
545	#else
546	unlock(ring.submit_q.submit_lock);
547	#endif
548	if( ret < 0 ) {
549	return;
550	}
551
552	// Release the consumed SQEs
553	__release_consumed_submission( ring );
554
555	// update statistics
556	__STATS__( false,
557	io.submit_q.submit_avg.rdy += to_submit;
558	io.submit_q.submit_avg.csm += ret;
559	io.submit_q.submit_avg.cnt += 1;
560	)
561
562	__cfadbg_print_safe( io, "Kernel I/O : submitted %u (among %u) for %p\n", idx, ret, active_thread() );
563	}
564	else
565	{
566	// get mutual exclusion
567	#if defined(LEADER_LOCK)
568	while(!try_lock(ring.submit_q.submit_lock));
569	#else
570	lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2);
571	#endif
572
573	/* paranoid */ verifyf( ring.submit_q.sqes[ idx ].user_data != 3ul64,
574	/* paranoid */ "index %u already reclaimed\n"
575	/* paranoid */ "head %u, prev %u, tail %u\n"
576	/* paranoid */ "[-0: %u,-1: %u,-2: %u,-3: %u]\n",
577	/* paranoid */ idx,
578	/* paranoid / ring.submit_q.head, ring.submit_q.prev_head, *tail
579	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 0) & (*ring.submit_q.mask) ]
580	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 1) & (*ring.submit_q.mask) ]
581	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 2) & (*ring.submit_q.mask) ]
582	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 3) & (*ring.submit_q.mask) ]
583	/* paranoid */ );
584
585	// Append to the list of ready entries
586
587	/* paranoid */ verify( idx <= mask );
588	ring.submit_q.array[ (*tail) & mask ] = idx;
589	__atomic_fetch_add(tail, 1ul32, __ATOMIC_SEQ_CST);
590
591	// Submit however, many entries need to be submitted
592	int ret = __io_uring_enter( ring, 1, false );
593	if( ret < 0 ) {
594	switch((int)errno) {
595	default:
596	abort( "KERNEL ERROR: IO_URING SUBMIT - %s\n", strerror(errno) );
597	}
598	}
599
600	/* paranoid */ verify(ret == 1);
601
602	// update statistics
603	__STATS__( false,
604	io.submit_q.submit_avg.csm += 1;
605	io.submit_q.submit_avg.cnt += 1;
606	)
607
608	{
609	__attribute__((unused)) volatile __u32 * const head = ring.submit_q.head;
610	__attribute__((unused)) __u32 last_idx = ring.submit_q.array[ ((*head) - 1) & mask ];
611	__attribute__((unused)) volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[last_idx];
612
613	__cfadbg_print_safe( io,
614	"Kernel I/O : last submitted is %u (%p)\n"
615	" data: %p\n"
616	" opcode: %s\n"
617	" fd: %d\n"
618	" flags: %d\n"
619	" prio: %d\n"
620	" off: %p\n"
621	" addr: %p\n"
622	" len: %d\n"
623	" other flags: %d\n"
624	" splice fd: %d\n"
625	" pad[0]: %llu\n"
626	" pad[1]: %llu\n"
627	" pad[2]: %llu\n",
628	last_idx, sqe,
629	(void*)sqe->user_data,
630	opcodes[sqe->opcode],
631	sqe->fd,
632	sqe->flags,
633	sqe->ioprio,
634	(void*)sqe->off,
635	(void*)sqe->addr,
636	sqe->len,
637	sqe->accept_flags,
638	sqe->splice_fd_in,
639	sqe->__pad2[0],
640	sqe->__pad2[1],
641	sqe->__pad2[2]
642	);
643	}
644
645	__atomic_thread_fence( __ATOMIC_SEQ_CST );
646	// Release the consumed SQEs
647
648	__release_consumed_submission( ring );
649	// ring.submit_q.sqes[idx].user_data = 3ul64;
650
651	#if defined(LEADER_LOCK)
652	next(ring.submit_q.submit_lock);
653	#else
654	unlock(ring.submit_q.submit_lock);
655	#endif
656
657	__cfadbg_print_safe( io, "Kernel I/O : submitted %u for %p\n", idx, active_thread() );
658	}
659	}
660
661	// #define PARTIAL_SUBMIT 32
662
663	// go through the list of submissions in the ready array and moved them into
664	// the ring's submit queue
665	static unsigned __collect_submitions( struct __io_data & ring ) {
666	/* paranoid */ verify( ring.submit_q.ready != 0p );
667	/* paranoid */ verify( ring.submit_q.ready_cnt > 0 );
668
669	unsigned to_submit = 0;
670	__u32 tail = *ring.submit_q.tail;
671	const __u32 mask = *ring.submit_q.mask;
672	#if defined(PARTIAL_SUBMIT)
673	#if defined(LEADER_LOCK)
674	#error PARTIAL_SUBMIT and LEADER_LOCK cannot co-exist
675	#endif
676	const __u32 cnt = ring.submit_q.ready_cnt > PARTIAL_SUBMIT ? PARTIAL_SUBMIT : ring.submit_q.ready_cnt;
677	const __u32 offset = ring.submit_q.prev_ready;
678	ring.submit_q.prev_ready += cnt;
679	#else
680	const __u32 cnt = ring.submit_q.ready_cnt;
681	const __u32 offset = 0;
682	#endif
683
684	// Go through the list of ready submissions
685	for( c; cnt ) {
686	__u32 i = (offset + c) % ring.submit_q.ready_cnt;
687
688	// replace any submission with the sentinel, to consume it.
689	__u32 idx = __atomic_exchange_n( &ring.submit_q.ready[i], -1ul32, __ATOMIC_RELAXED);
690
691	// If it was already the sentinel, then we are done
692	if( idx == -1ul32 ) continue;
693
694	// If we got a real submission, append it to the list
695	ring.submit_q.array[ (tail + to_submit) & mask ] = idx & mask;
696	to_submit++;
697	}
698
699	// Increment the tail based on how many we are ready to submit
700	__atomic_fetch_add(ring.submit_q.tail, to_submit, __ATOMIC_SEQ_CST);
701
702	return to_submit;
703	}
704
705	// Go through the ring's submit queue and release everything that has already been consumed
706	// by io_uring
707	static __u32 __release_consumed_submission( struct __io_data & ring ) {
708	const __u32 smask = *ring.submit_q.mask;
709
710	// We need to get the lock to copy the old head and new head
711	if( !try_lock(ring.submit_q.release_lock __cfaabi_dbg_ctx2) ) return 0;
712	__attribute__((unused))
713	__u32 ctail = *ring.submit_q.tail; // get the current tail of the queue
714	__u32 chead = *ring.submit_q.head; // get the current head of the queue
715	__u32 phead = ring.submit_q.prev_head; // get the head the last time we were here
716	ring.submit_q.prev_head = chead; // note up to were we processed
717	unlock(ring.submit_q.release_lock);
718
719	// the 3 fields are organized like this diagram
720	// except it's are ring
721	// ---+--------+--------+----
722	// ---+--------+--------+----
723	// ^ ^ ^
724	// phead chead ctail
725
726	// make sure ctail doesn't wrap around and reach phead
727	/* paranoid */ verify(
728	(ctail >= chead && chead >= phead)
729	\|\| (chead >= phead && phead >= ctail)
730	\|\| (phead >= ctail && ctail >= chead)
731	);
732
733	// find the range we need to clear
734	__u32 count = chead - phead;
735
736	// We acquired an previous-head/current-head range
737	// go through the range and release the sqes
738	for( i; count ) {
739	__u32 idx = ring.submit_q.array[ (phead + i) & smask ];
740
741	/* paranoid */ verify( 0 != ring.submit_q.sqes[ idx ].user_data );
742	__clean( &ring.submit_q.sqes[ idx ] );
743	}
744	return count;
745	}
746
747	void __sqe_clean( volatile struct io_uring_sqe * sqe ) {
748	__clean( sqe );
749	}
750
751	static inline void __clean( volatile struct io_uring_sqe * sqe ) {
752	// If we are in debug mode, thrash the fields to make sure we catch reclamation errors
753	__cfaabi_dbg_debug_do(
754	memset(sqe, 0xde, sizeof(*sqe));
755	sqe->opcode = (sizeof(opcodes) / sizeof(const char *)) - 1;
756	);
757
758	// Mark the entry as unused
759	__atomic_store_n(&sqe->user_data, 3ul64, __ATOMIC_SEQ_CST);
760	}
761	#endif

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