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ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum

Last change on this file since d48b174 was d48b174, checked in by Thierry Delisle <tdelisle@…>, 5 years ago
clean-up handling of epoll so it's limited to one file
Property mode set to `100644`
File size: 21.0 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
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	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	if( ret < 0 ) {
176	switch((int)errno) {
177	case EAGAIN:
178	case EINTR:
179	ret = -1;
180	break;
181	default:
182	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
183	}
184	}
185	}
186
187	// Memory barrier
188	__atomic_thread_fence( __ATOMIC_SEQ_CST );
189	return ret;
190	}
191
192	//=============================================================================================
193	// I/O Polling
194	//=============================================================================================
195	static unsigned __collect_submitions( struct __io_data & ring );
196	static __u32 __release_consumed_submission( struct __io_data & ring );
197
198	// Process a single completion message from the io_uring
199	// This is NOT thread-safe
200	static inline void process( volatile struct io_uring_cqe & cqe ) {
201	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
202	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
203
204	fulfil( *future, cqe.res );
205	}
206
207	static [int, bool] __drain_io( & struct __io_data ring ) {
208	/* paranoid */ verify( ! __preemption_enabled() );
209
210	unsigned to_submit = 0;
211	if( ring.poller_submits ) {
212	// If the poller thread also submits, then we need to aggregate the submissions which are ready
213	to_submit = __collect_submitions( ring );
214	}
215
216	int ret = __io_uring_enter(ring, to_submit, true);
217	if( ret < 0 ) {
218	return [0, true];
219	}
220
221	// update statistics
222	if (to_submit > 0) {
223	__STATS__( true,
224	if( to_submit > 0 ) {
225	io.submit_q.submit_avg.rdy += to_submit;
226	io.submit_q.submit_avg.csm += ret;
227	io.submit_q.submit_avg.cnt += 1;
228	}
229	)
230	}
231
232	__atomic_thread_fence( __ATOMIC_SEQ_CST );
233
234	// Release the consumed SQEs
235	__release_consumed_submission( ring );
236
237	// Drain the queue
238	unsigned head = *ring.completion_q.head;
239	unsigned tail = *ring.completion_q.tail;
240	const __u32 mask = *ring.completion_q.mask;
241
242	// Nothing was new return 0
243	if (head == tail) {
244	return [0, to_submit > 0];
245	}
246
247	__u32 count = tail - head;
248	/* paranoid */ verify( count != 0 );
249	for(i; count) {
250	unsigned idx = (head + i) & mask;
251	volatile struct io_uring_cqe & cqe = ring.completion_q.cqes[idx];
252
253	/* paranoid */ verify(&cqe);
254
255	process( cqe );
256	}
257
258	// Mark to the kernel that the cqe has been seen
259	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
260	__atomic_fetch_add( ring.completion_q.head, count, __ATOMIC_SEQ_CST );
261
262	return [count, count > 0 \|\| to_submit > 0];
263	}
264
265	void main( $io_ctx_thread & this ) {
266	__ioctx_register( this );
267
268	__cfadbg_print_safe(io_core, "Kernel I/O : IO poller %d (%p) ready\n", this.ring->fd, &this);
269
270	const int reset_cnt = 5;
271	int reset = reset_cnt;
272	// Then loop until we need to start
273	LOOP:
274	while(!__atomic_load_n(&this.done, __ATOMIC_SEQ_CST)) {
275	// Drain the io
276	int count;
277	bool again;
278	disable_interrupts();
279	[count, again] = __drain_io( *this.ring );
280
281	if(!again) reset--;
282
283	// Update statistics
284	__STATS__( true,
285	io.complete_q.completed_avg.val += count;
286	io.complete_q.completed_avg.cnt += 1;
287	)
288	enable_interrupts( __cfaabi_dbg_ctx );
289
290	// If we got something, just yield and check again
291	if(reset > 1) {
292	yield();
293	continue LOOP;
294	}
295
296	// We alread failed to find completed entries a few time.
297	if(reset == 1) {
298	// Rearm the context so it can block
299	// but don't block right away
300	// we need to retry one last time in case
301	// something completed just now
302	__ioctx_prepare_block( this );
303	continue LOOP;
304	}
305
306	__STATS__( false,
307	io.complete_q.blocks += 1;
308	)
309	__cfadbg_print_safe(io_core, "Kernel I/O : Parking io poller %d (%p)\n", this.ring->fd, &this);
310
311	// block this thread
312	wait( this.sem );
313
314	// restore counter
315	reset = reset_cnt;
316	}
317
318	__cfadbg_print_safe(io_core, "Kernel I/O : Fast poller %d (%p) stopping\n", this.ring->fd, &this);
319	}
320
321	//=============================================================================================
322	// I/O Submissions
323	//=============================================================================================
324
325	// Submition steps :
326	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
327	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
328	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
329	// need to write an allocator that allows allocating concurrently.
330	//
331	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
332	//
333	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
334	// needs to arrive to two concensus at the same time:
335	// A - The order in which entries are listed in the array: no two threads must pick the
336	// same index for their entries
337	// B - When can the tail be update for the kernel. EVERY entries in the array between
338	// head and tail must be fully filled and shouldn't ever be touched again.
339	//
340
341	// Allocate an submit queue entry.
342	// The kernel cannot see these entries until they are submitted, but other threads must be
343	// able to see which entries can be used and which are already un used by an other thread
344	// for convenience, return both the index and the pointer to the sqe
345	// sqe == &sqes[idx]
346	[* volatile struct io_uring_sqe, __u32] __submit_alloc( struct __io_data & ring, __u64 data ) {
347	/* paranoid */ verify( data != 0 );
348
349	// Prepare the data we need
350	__attribute((unused)) int len = 0;
351	__attribute((unused)) int block = 0;
352	__u32 cnt = *ring.submit_q.num;
353	__u32 mask = *ring.submit_q.mask;
354
355	__u32 off = thread_rand();
356
357	// Loop around looking for an available spot
358	for() {
359	// Look through the list starting at some offset
360	for(i; cnt) {
361	__u64 expected = 3;
362	__u32 idx = (i + off) & mask; // Get an index from a random
363	volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
364	volatile __u64 * udata = &sqe->user_data;
365
366	// Allocate the entry by CASing the user_data field from 0 to the future address
367	if( *udata == expected &&
368	__atomic_compare_exchange_n( udata, &expected, data, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) )
369	{
370	// update statistics
371	__STATS__( false,
372	io.submit_q.alloc_avg.val += len;
373	io.submit_q.alloc_avg.block += block;
374	io.submit_q.alloc_avg.cnt += 1;
375	)
376
377	// debug log
378	__cfadbg_print_safe( io, "Kernel I/O : allocated [%p, %u] for %p (%p)\n", sqe, idx, active_thread(), (void*)data );
379
380	// Success return the data
381	sqe->opcode = 0;
382	sqe->flags = 0;
383	sqe->ioprio = 0;
384	sqe->fd = 0;
385	sqe->off = 0;
386	sqe->addr = 0;
387	sqe->len = 0;
388	sqe->accept_flags = 0;
389	sqe->__pad2[0] = 0;
390	sqe->__pad2[1] = 0;
391	sqe->__pad2[2] = 0;
392	return [sqe, idx];
393	}
394	verify(expected != data);
395
396	// This one was used
397	len ++;
398	}
399
400	block++;
401
402	abort( "Kernel I/O : all submit queue entries used, yielding\n" );
403
404	yield();
405	}
406	}
407
408	static inline __u32 __submit_to_ready_array( struct __io_data & ring, __u32 idx, const __u32 mask ) {
409	/* paranoid */ verify( idx <= mask );
410	/* paranoid */ verify( idx != -1ul32 );
411
412	// We need to find a spot in the ready array
413	__attribute((unused)) int len = 0;
414	__attribute((unused)) int block = 0;
415	__u32 ready_mask = ring.submit_q.ready_cnt - 1;
416
417	__u32 off = thread_rand();
418
419	__u32 picked;
420	LOOKING: for() {
421	for(i; ring.submit_q.ready_cnt) {
422	picked = (i + off) & ready_mask;
423	__u32 expected = -1ul32;
424	if( __atomic_compare_exchange_n( &ring.submit_q.ready[picked], &expected, idx, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) ) {
425	break LOOKING;
426	}
427	verify(expected != idx);
428
429	len ++;
430	}
431
432	block++;
433
434	__u32 released = __release_consumed_submission( ring );
435	if( released == 0 ) {
436	yield();
437	}
438	}
439
440	// update statistics
441	__STATS__( false,
442	io.submit_q.look_avg.val += len;
443	io.submit_q.look_avg.block += block;
444	io.submit_q.look_avg.cnt += 1;
445	)
446
447	return picked;
448	}
449
450	void __submit( struct io_context * ctx, __u32 idx ) __attribute__((nonnull (1))) {
451	__io_data & ring = *ctx->thrd.ring;
452
453	{
454	__attribute__((unused)) volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
455	__cfadbg_print_safe( io,
456	"Kernel I/O : submitting %u (%p) for %p\n"
457	" data: %p\n"
458	" opcode: %s\n"
459	" fd: %d\n"
460	" flags: %d\n"
461	" prio: %d\n"
462	" off: %p\n"
463	" addr: %p\n"
464	" len: %d\n"
465	" other flags: %d\n"
466	" splice fd: %d\n"
467	" pad[0]: %llu\n"
468	" pad[1]: %llu\n"
469	" pad[2]: %llu\n",
470	idx, sqe,
471	active_thread(),
472	(void*)sqe->user_data,
473	opcodes[sqe->opcode],
474	sqe->fd,
475	sqe->flags,
476	sqe->ioprio,
477	sqe->off,
478	sqe->addr,
479	sqe->len,
480	sqe->accept_flags,
481	sqe->splice_fd_in,
482	sqe->__pad2[0],
483	sqe->__pad2[1],
484	sqe->__pad2[2]
485	);
486	}
487
488
489	// Get now the data we definetely need
490	volatile __u32 * const tail = ring.submit_q.tail;
491	const __u32 mask = *ring.submit_q.mask;
492
493	// There are 2 submission schemes, check which one we are using
494	if( ring.poller_submits ) {
495	// If the poller thread submits, then we just need to add this to the ready array
496	__submit_to_ready_array( ring, idx, mask );
497
498	post( ctx->thrd.sem );
499
500	__cfadbg_print_safe( io, "Kernel I/O : Added %u to ready for %p\n", idx, active_thread() );
501	}
502	else if( ring.eager_submits ) {
503	__u32 picked = __submit_to_ready_array( ring, idx, mask );
504
505	#if defined(LEADER_LOCK)
506	if( !try_lock(ring.submit_q.submit_lock) ) {
507	__STATS__( false,
508	io.submit_q.helped += 1;
509	)
510	return;
511	}
512	/* paranoid */ verify( ! __preemption_enabled() );
513	__STATS__( true,
514	io.submit_q.leader += 1;
515	)
516	#else
517	for() {
518	yield();
519
520	if( try_lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2) ) {
521	__STATS__( false,
522	io.submit_q.leader += 1;
523	)
524	break;
525	}
526
527	// If some one else collected our index, we are done
528	#warning ABA problem
529	if( ring.submit_q.ready[picked] != idx ) {
530	__STATS__( false,
531	io.submit_q.helped += 1;
532	)
533	return;
534	}
535
536	__STATS__( false,
537	io.submit_q.busy += 1;
538	)
539	}
540	#endif
541
542	// We got the lock
543	// Collect the submissions
544	unsigned to_submit = __collect_submitions( ring );
545
546	// Actually submit
547	int ret = __io_uring_enter( ring, to_submit, false );
548
549	#if defined(LEADER_LOCK)
550	/* paranoid */ verify( ! __preemption_enabled() );
551	next(ring.submit_q.submit_lock);
552	#else
553	unlock(ring.submit_q.submit_lock);
554	#endif
555	if( ret < 0 ) {
556	return;
557	}
558
559	// Release the consumed SQEs
560	__release_consumed_submission( ring );
561
562	// update statistics
563	__STATS__( false,
564	io.submit_q.submit_avg.rdy += to_submit;
565	io.submit_q.submit_avg.csm += ret;
566	io.submit_q.submit_avg.cnt += 1;
567	)
568
569	__cfadbg_print_safe( io, "Kernel I/O : submitted %u (among %u) for %p\n", idx, ret, active_thread() );
570	}
571	else
572	{
573	// get mutual exclusion
574	#if defined(LEADER_LOCK)
575	while(!try_lock(ring.submit_q.submit_lock));
576	#else
577	lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2);
578	#endif
579
580	/* paranoid */ verifyf( ring.submit_q.sqes[ idx ].user_data != 3ul64,
581	/* paranoid */ "index %u already reclaimed\n"
582	/* paranoid */ "head %u, prev %u, tail %u\n"
583	/* paranoid */ "[-0: %u,-1: %u,-2: %u,-3: %u]\n",
584	/* paranoid */ idx,
585	/* paranoid / ring.submit_q.head, ring.submit_q.prev_head, *tail
586	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 0) & (*ring.submit_q.mask) ]
587	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 1) & (*ring.submit_q.mask) ]
588	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 2) & (*ring.submit_q.mask) ]
589	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 3) & (*ring.submit_q.mask) ]
590	/* paranoid */ );
591
592	// Append to the list of ready entries
593
594	/* paranoid */ verify( idx <= mask );
595	ring.submit_q.array[ (*tail) & mask ] = idx;
596	__atomic_fetch_add(tail, 1ul32, __ATOMIC_SEQ_CST);
597
598	// Submit however, many entries need to be submitted
599	int ret = __io_uring_enter( ring, 1, false );
600	if( ret < 0 ) {
601	switch((int)errno) {
602	default:
603	abort( "KERNEL ERROR: IO_URING SUBMIT - %s\n", strerror(errno) );
604	}
605	}
606
607	/* paranoid */ verify(ret == 1);
608
609	// update statistics
610	__STATS__( false,
611	io.submit_q.submit_avg.csm += 1;
612	io.submit_q.submit_avg.cnt += 1;
613	)
614
615	{
616	__attribute__((unused)) volatile __u32 * const head = ring.submit_q.head;
617	__attribute__((unused)) __u32 last_idx = ring.submit_q.array[ ((*head) - 1) & mask ];
618	__attribute__((unused)) volatile struct io_uring_sqe * sqe = &ring.submit_q.sqes[last_idx];
619
620	__cfadbg_print_safe( io,
621	"Kernel I/O : last submitted is %u (%p)\n"
622	" data: %p\n"
623	" opcode: %s\n"
624	" fd: %d\n"
625	" flags: %d\n"
626	" prio: %d\n"
627	" off: %p\n"
628	" addr: %p\n"
629	" len: %d\n"
630	" other flags: %d\n"
631	" splice fd: %d\n"
632	" pad[0]: %llu\n"
633	" pad[1]: %llu\n"
634	" pad[2]: %llu\n",
635	last_idx, sqe,
636	(void*)sqe->user_data,
637	opcodes[sqe->opcode],
638	sqe->fd,
639	sqe->flags,
640	sqe->ioprio,
641	sqe->off,
642	sqe->addr,
643	sqe->len,
644	sqe->accept_flags,
645	sqe->splice_fd_in,
646	sqe->__pad2[0],
647	sqe->__pad2[1],
648	sqe->__pad2[2]
649	);
650	}
651
652	__atomic_thread_fence( __ATOMIC_SEQ_CST );
653	// Release the consumed SQEs
654	__release_consumed_submission( ring );
655	// ring.submit_q.sqes[idx].user_data = 3ul64;
656
657	#if defined(LEADER_LOCK)
658	next(ring.submit_q.submit_lock);
659	#else
660	unlock(ring.submit_q.submit_lock);
661	#endif
662
663	__cfadbg_print_safe( io, "Kernel I/O : submitted %u for %p\n", idx, active_thread() );
664	}
665	}
666
667	// #define PARTIAL_SUBMIT 32
668
669	// go through the list of submissions in the ready array and moved them into
670	// the ring's submit queue
671	static unsigned __collect_submitions( struct __io_data & ring ) {
672	/* paranoid */ verify( ring.submit_q.ready != 0p );
673	/* paranoid */ verify( ring.submit_q.ready_cnt > 0 );
674
675	unsigned to_submit = 0;
676	__u32 tail = *ring.submit_q.tail;
677	const __u32 mask = *ring.submit_q.mask;
678	#if defined(PARTIAL_SUBMIT)
679	#if defined(LEADER_LOCK)
680	#error PARTIAL_SUBMIT and LEADER_LOCK cannot co-exist
681	#endif
682	const __u32 cnt = ring.submit_q.ready_cnt > PARTIAL_SUBMIT ? PARTIAL_SUBMIT : ring.submit_q.ready_cnt;
683	const __u32 offset = ring.submit_q.prev_ready;
684	ring.submit_q.prev_ready += cnt;
685	#else
686	const __u32 cnt = ring.submit_q.ready_cnt;
687	const __u32 offset = 0;
688	#endif
689
690	// Go through the list of ready submissions
691	for( c; cnt ) {
692	__u32 i = (offset + c) % ring.submit_q.ready_cnt;
693
694	// replace any submission with the sentinel, to consume it.
695	__u32 idx = __atomic_exchange_n( &ring.submit_q.ready[i], -1ul32, __ATOMIC_RELAXED);
696
697	// If it was already the sentinel, then we are done
698	if( idx == -1ul32 ) continue;
699
700	// If we got a real submission, append it to the list
701	ring.submit_q.array[ (tail + to_submit) & mask ] = idx & mask;
702	to_submit++;
703	}
704
705	// Increment the tail based on how many we are ready to submit
706	__atomic_fetch_add(ring.submit_q.tail, to_submit, __ATOMIC_SEQ_CST);
707
708	return to_submit;
709	}
710
711	// Go through the ring's submit queue and release everything that has already been consumed
712	// by io_uring
713	static __u32 __release_consumed_submission( struct __io_data & ring ) {
714	const __u32 smask = *ring.submit_q.mask;
715
716	// We need to get the lock to copy the old head and new head
717	if( !try_lock(ring.submit_q.release_lock __cfaabi_dbg_ctx2) ) return 0;
718	__attribute__((unused))
719	__u32 ctail = *ring.submit_q.tail; // get the current tail of the queue
720	__u32 chead = *ring.submit_q.head; // get the current head of the queue
721	__u32 phead = ring.submit_q.prev_head; // get the head the last time we were here
722	ring.submit_q.prev_head = chead; // note up to were we processed
723	unlock(ring.submit_q.release_lock);
724
725	// the 3 fields are organized like this diagram
726	// except it's are ring
727	// ---+--------+--------+----
728	// ---+--------+--------+----
729	// ^ ^ ^
730	// phead chead ctail
731
732	// make sure ctail doesn't wrap around and reach phead
733	/* paranoid */ verify(
734	(ctail >= chead && chead >= phead)
735	\|\| (chead >= phead && phead >= ctail)
736	\|\| (phead >= ctail && ctail >= chead)
737	);
738
739	// find the range we need to clear
740	__u32 count = chead - phead;
741
742	// We acquired an previous-head/current-head range
743	// go through the range and release the sqes
744	for( i; count ) {
745	__u32 idx = ring.submit_q.array[ (phead + i) & smask ];
746
747	/* paranoid */ verify( 0 != ring.submit_q.sqes[ idx ].user_data );
748	ring.submit_q.sqes[ idx ].user_data = 3ul64;
749	}
750	return count;
751	}
752	#endif

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