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io.cfa @ dcb5f8d

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

Last change on this file since dcb5f8d was dcb5f8d, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
Added statistics for the number of times io_ctxs blocked
Property mode set to `100644`
File size: 15.9 KB

Rev	Line
[ecf6b46]	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
[3e2b9c9]	16	#define __cforall_thread__
	17
[20ab637]	18	#if defined(__CFA_DEBUG__)
	19	// #define __CFA_DEBUG_PRINT_IO__
[e660761]	20	// #define __CFA_DEBUG_PRINT_IO_CORE__
[20ab637]	21	#endif
[4069faad]	22
[f6660520]	23
[3e2b9c9]	24	#if defined(CFA_HAVE_LINUX_IO_URING_H)
[31bb2e1]	25	#define _GNU_SOURCE /* See feature_test_macros(7) */
	26	#include <errno.h>
[3e2b9c9]	27	#include <signal.h>
[31bb2e1]	28	#include <stdint.h>
	29	#include <string.h>
	30	#include <unistd.h>
	31
[92976d9]	32	extern "C" {
[f00b26d4]	33	#include <sys/epoll.h>
[92976d9]	34	#include <sys/syscall.h>
	35
	36	#include <linux/io_uring.h>
	37	}
	38
[3e2b9c9]	39	#include "stats.hfa"
	40	#include "kernel.hfa"
	41	#include "kernel/fwd.hfa"
	42	#include "io/types.hfa"
[185efe6]	43
[2fafe7e]	44	// returns true of acquired as leader or second leader
	45	static inline bool try_lock( __leaderlock_t & this ) {
	46	const uintptr_t thrd = 1z \| (uintptr_t)active_thread();
	47	bool block;
	48	disable_interrupts();
	49	for() {
	50	struct $thread * expected = this.value;
	51	if( 1p != expected && 0p != expected ) {
	52	/* paranoid */ verify( thrd != (uintptr_t)expected ); // We better not already be the next leader
	53	enable_interrupts( __cfaabi_dbg_ctx );
	54	return false;
	55	}
	56	struct $thread * desired;
	57	if( 0p == expected ) {
	58	// If the lock isn't locked acquire it, no need to block
	59	desired = 1p;
	60	block = false;
	61	}
	62	else {
	63	// If the lock is already locked try becomming the next leader
	64	desired = (struct $thread *)thrd;
	65	block = true;
	66	}
	67	if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
	68	}
	69	if( block ) {
	70	enable_interrupts( __cfaabi_dbg_ctx );
	71	park( __cfaabi_dbg_ctx );
	72	disable_interrupts();
	73	}
	74	return true;
	75	}
	76
	77	static inline bool next( __leaderlock_t & this ) {
	78	/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
	79	struct $thread * nextt;
	80	for() {
	81	struct $thread * expected = this.value;
	82	/* paranoid */ verify( (1 & (uintptr_t)expected) == 1 ); // The lock better be locked
	83
	84	struct $thread * desired;
	85	if( 1p == expected ) {
	86	// No next leader, just unlock
	87	desired = 0p;
	88	nextt = 0p;
	89	}
	90	else {
	91	// There is a next leader, remove but keep locked
	92	desired = 1p;
	93	nextt = (struct $thread *)(~1z & (uintptr_t)expected);
	94	}
	95	if( __atomic_compare_exchange_n(&this.value, &expected, desired, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ) break;
	96	}
	97
	98	if(nextt) {
	99	unpark( nextt __cfaabi_dbg_ctx2 );
	100	enable_interrupts( __cfaabi_dbg_ctx );
	101	return true;
	102	}
	103	enable_interrupts( __cfaabi_dbg_ctx );
	104	return false;
	105	}
	106
[92976d9]	107	//=============================================================================================
[3e2b9c9]	108	// I/O Syscall
[92976d9]	109	//=============================================================================================
[3e2b9c9]	110	static int __io_uring_enter( struct __io_data & ring, unsigned to_submit, bool get ) {
[20ab637]	111	bool need_sys_to_submit = false;
	112	bool need_sys_to_complete = false;
	113	unsigned flags = 0;
	114
	115	TO_SUBMIT:
	116	if( to_submit > 0 ) {
	117	if( !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
	118	need_sys_to_submit = true;
	119	break TO_SUBMIT;
	120	}
	121	if( (*ring.submit_q.flags) & IORING_SQ_NEED_WAKEUP ) {
	122	need_sys_to_submit = true;
	123	flags \|= IORING_ENTER_SQ_WAKEUP;
	124	}
	125	}
	126
	127	if( get && !(ring.ring_flags & IORING_SETUP_SQPOLL) ) {
	128	flags \|= IORING_ENTER_GETEVENTS;
	129	if( (ring.ring_flags & IORING_SETUP_IOPOLL) ) {
	130	need_sys_to_complete = true;
	131	}
	132	}
	133
	134	int ret = 0;
	135	if( need_sys_to_submit \|\| need_sys_to_complete ) {
[f00b26d4]	136	ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, 0, flags, 0p, _NSIG / 8);
[20ab637]	137	if( ret < 0 ) {
	138	switch((int)errno) {
	139	case EAGAIN:
	140	case EINTR:
	141	ret = -1;
	142	break;
	143	default:
	144	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
	145	}
	146	}
	147	}
	148
	149	// Memory barrier
	150	__atomic_thread_fence( __ATOMIC_SEQ_CST );
	151	return ret;
	152	}
	153
[92976d9]	154	//=============================================================================================
	155	// I/O Polling
	156	//=============================================================================================
[1d5e4711]	157	static unsigned __collect_submitions( struct __io_data & ring );
[4998155]	158	static __u32 __release_consumed_submission( struct __io_data & ring );
[1d5e4711]	159
[f00b26d4]	160	static inline void process(struct io_uring_cqe & cqe ) {
[5751a56]	161	struct __io_user_data_t * data = (struct __io_user_data_t *)(uintptr_t)cqe.user_data;
	162	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", data, cqe.res, data->thrd );
	163
	164	data->result = cqe.res;
[4998155]	165	post( data->sem );
[5751a56]	166	}
	167
[92976d9]	168	// Process a single completion message from the io_uring
	169	// This is NOT thread-safe
[f00b26d4]	170	static [int, bool] __drain_io( & struct __io_data ring ) {
[e46c753]	171	/* paranoid */ verify( !kernelTLS.preemption_state.enabled );
	172
[5dadc9b]	173	unsigned to_submit = 0;
[f00b26d4]	174	if( ring.poller_submits ) {
[5dadc9b]	175	// If the poller thread also submits, then we need to aggregate the submissions which are ready
[e46c753]	176	to_submit = __collect_submitions( ring );
[5dadc9b]	177	}
	178
[f00b26d4]	179	int ret = __io_uring_enter(ring, to_submit, true);
[20ab637]	180	if( ret < 0 ) {
	181	return [0, true];
	182	}
[1d5e4711]	183
[20ab637]	184	// update statistics
	185	if (to_submit > 0) {
[1d5e4711]	186	__STATS__( true,
	187	if( to_submit > 0 ) {
	188	io.submit_q.submit_avg.rdy += to_submit;
	189	io.submit_q.submit_avg.csm += ret;
	190	io.submit_q.submit_avg.cnt += 1;
	191	}
	192	)
[6f121b8]	193	}
	194
[20ab637]	195	// Release the consumed SQEs
	196	__release_consumed_submission( ring );
[6f121b8]	197
[d384787]	198	// Drain the queue
[92976d9]	199	unsigned head = *ring.completion_q.head;
[6f121b8]	200	unsigned tail = *ring.completion_q.tail;
[4998155]	201	const __u32 mask = *ring.completion_q.mask;
[6f121b8]	202
[d384787]	203	// Nothing was new return 0
	204	if (head == tail) {
[e46c753]	205	return [0, to_submit > 0];
[d384787]	206	}
[92976d9]	207
[4998155]	208	__u32 count = tail - head;
[1d5e4711]	209	/* paranoid */ verify( count != 0 );
[d384787]	210	for(i; count) {
[6f121b8]	211	unsigned idx = (head + i) & mask;
[d384787]	212	struct io_uring_cqe & cqe = ring.completion_q.cqes[idx];
[92976d9]	213
[d384787]	214	/* paranoid */ verify(&cqe);
[92976d9]	215
[f00b26d4]	216	process( cqe );
[d384787]	217	}
[2d8f7b0]	218
[92976d9]	219	// Mark to the kernel that the cqe has been seen
	220	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
[6f121b8]	221	__atomic_thread_fence( __ATOMIC_SEQ_CST );
[d384787]	222	__atomic_fetch_add( ring.completion_q.head, count, __ATOMIC_RELAXED );
[92976d9]	223
[5dadc9b]	224	return [count, count > 0 \|\| to_submit > 0];
[92976d9]	225	}
	226
[f00b26d4]	227	void main( $io_ctx_thread & this ) {
	228	epoll_event ev;
[3e2b9c9]	229	__ioctx_register( this, ev );
[1539bbd]	230
[f00b26d4]	231	__cfadbg_print_safe(io_core, "Kernel I/O : IO poller %p for ring %p ready\n", &this, &this.ring);
[1539bbd]	232
[4e74466]	233	int reset = 0;
[61dd73d]	234	// Then loop until we need to start
[f00b26d4]	235	while(!__atomic_load_n(&this.done, __ATOMIC_SEQ_CST)) {
[61dd73d]	236	// Drain the io
[5dadc9b]	237	int count;
	238	bool again;
[13c5e19]	239	disable_interrupts();
[f00b26d4]	240	[count, again] = __drain_io( *this.ring );
[5dadc9b]	241
[13c5e19]	242	if(!again) reset++;
[3c039b0]	243
[13c5e19]	244	// Update statistics
[47746a2]	245	__STATS__( true,
	246	io.complete_q.completed_avg.val += count;
[dcb5f8d]	247	io.complete_q.completed_avg.cnt += 1;
[47746a2]	248	)
[13c5e19]	249	enable_interrupts( __cfaabi_dbg_ctx );
[3c039b0]	250
[5dadc9b]	251	// If we got something, just yield and check again
[4e74466]	252	if(reset < 5) {
[61dd73d]	253	yield();
	254	}
[5dadc9b]	255	// We didn't get anything baton pass to the slow poller
[61dd73d]	256	else {
[dcb5f8d]	257	__STATS__( true,
	258	io.complete_q.blocks += 1;
	259	)
[f00b26d4]	260	__cfadbg_print_safe(io_core, "Kernel I/O : Parking io poller %p\n", &this.self);
[5dadc9b]	261	reset = 0;
	262
[3e2b9c9]	263	// block this thread
	264	__ioctx_prepare_block( this, ev );
[f00b26d4]	265	wait( this.sem );
[f6660520]	266	}
	267	}
[61dd73d]	268
	269	__cfadbg_print_safe(io_core, "Kernel I/O : Fast poller for ring %p stopping\n", &this.ring);
	270	}
[f6660520]	271
[92976d9]	272	//=============================================================================================
	273	// I/O Submissions
	274	//=============================================================================================
	275
[2d8f7b0]	276	// Submition steps :
[e46c753]	277	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
[2d8f7b0]	278	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
	279	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
	280	// need to write an allocator that allows allocating concurrently.
	281	//
[e46c753]	282	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
[2d8f7b0]	283	//
[e46c753]	284	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
[2d8f7b0]	285	// needs to arrive to two concensus at the same time:
	286	// A - The order in which entries are listed in the array: no two threads must pick the
	287	// same index for their entries
	288	// B - When can the tail be update for the kernel. EVERY entries in the array between
	289	// head and tail must be fully filled and shouldn't ever be touched again.
	290	//
	291
[4998155]	292	[* struct io_uring_sqe, __u32] __submit_alloc( struct __io_data & ring, __u64 data ) {
[e46c753]	293	/* paranoid */ verify( data != 0 );
[13c5e19]	294
[6f121b8]	295	// Prepare the data we need
	296	__attribute((unused)) int len = 0;
	297	__attribute((unused)) int block = 0;
[4998155]	298	__u32 cnt = *ring.submit_q.num;
	299	__u32 mask = *ring.submit_q.mask;
[8ae4165]	300
	301	disable_interrupts();
[4998155]	302	__u32 off = __tls_rand();
[8ae4165]	303	enable_interrupts( __cfaabi_dbg_ctx );
[6f121b8]	304
	305	// Loop around looking for an available spot
[13c5e19]	306	for() {
[6f121b8]	307	// Look through the list starting at some offset
	308	for(i; cnt) {
[4998155]	309	__u64 expected = 0;
	310	__u32 idx = (i + off) & mask;
[6f121b8]	311	struct io_uring_sqe * sqe = &ring.submit_q.sqes[idx];
[4998155]	312	volatile __u64 * udata = &sqe->user_data;
[6f121b8]	313
	314	if( *udata == expected &&
	315	__atomic_compare_exchange_n( udata, &expected, data, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) )
	316	{
	317	// update statistics
[47746a2]	318	__STATS__( false,
	319	io.submit_q.alloc_avg.val += len;
	320	io.submit_q.alloc_avg.block += block;
	321	io.submit_q.alloc_avg.cnt += 1;
	322	)
[6f121b8]	323
[13c5e19]	324
[6f121b8]	325	// Success return the data
	326	return [sqe, idx];
	327	}
	328	verify(expected != data);
[2489d31]	329
[6f121b8]	330	len ++;
	331	}
[2489d31]	332
[6f121b8]	333	block++;
	334	yield();
	335	}
[2489d31]	336	}
	337
[4998155]	338	static inline __u32 __submit_to_ready_array( struct __io_data & ring, __u32 idx, const __u32 mask ) {
[df40a56]	339	/* paranoid */ verify( idx <= mask );
	340	/* paranoid */ verify( idx != -1ul32 );
	341
	342	// We need to find a spot in the ready array
	343	__attribute((unused)) int len = 0;
	344	__attribute((unused)) int block = 0;
[4998155]	345	__u32 ready_mask = ring.submit_q.ready_cnt - 1;
[df40a56]	346
	347	disable_interrupts();
[4998155]	348	__u32 off = __tls_rand();
[df40a56]	349	enable_interrupts( __cfaabi_dbg_ctx );
	350
[4998155]	351	__u32 picked;
[df40a56]	352	LOOKING: for() {
	353	for(i; ring.submit_q.ready_cnt) {
	354	picked = (i + off) & ready_mask;
[4998155]	355	__u32 expected = -1ul32;
[df40a56]	356	if( __atomic_compare_exchange_n( &ring.submit_q.ready[picked], &expected, idx, true, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED ) ) {
	357	break LOOKING;
	358	}
	359	verify(expected != idx);
	360
	361	len ++;
	362	}
	363
	364	block++;
[2fafe7e]	365
	366	__u32 released = __release_consumed_submission( ring );
	367	if( released == 0 ) {
[34b61882]	368	yield();
	369	}
[df40a56]	370	}
	371
	372	// update statistics
[47746a2]	373	__STATS__( false,
	374	io.submit_q.look_avg.val += len;
	375	io.submit_q.look_avg.block += block;
	376	io.submit_q.look_avg.cnt += 1;
	377	)
[df40a56]	378
	379	return picked;
	380	}
	381
[4998155]	382	void __submit( struct io_context * ctx, __u32 idx ) __attribute__((nonnull (1))) {
[f00b26d4]	383	__io_data & ring = *ctx->thrd.ring;
[5dadc9b]	384	// Get now the data we definetely need
[4998155]	385	volatile __u32 * const tail = ring.submit_q.tail;
	386	const __u32 mask = *ring.submit_q.mask;
[2489d31]	387
[5dadc9b]	388	// There are 2 submission schemes, check which one we are using
[f00b26d4]	389	if( ring.poller_submits ) {
[5dadc9b]	390	// If the poller thread submits, then we just need to add this to the ready array
[df40a56]	391	__submit_to_ready_array( ring, idx, mask );
[5dadc9b]	392
[f00b26d4]	393	post( ctx->thrd.sem );
[5dadc9b]	394
[dd4e2d7]	395	__cfadbg_print_safe( io, "Kernel I/O : Added %u to ready for %p\n", idx, active_thread() );
[2d8f7b0]	396	}
[f00b26d4]	397	else if( ring.eager_submits ) {
[4998155]	398	__u32 picked = __submit_to_ready_array( ring, idx, mask );
[e46c753]	399
[2fafe7e]	400	#if defined(LEADER_LOCK)
	401	if( !try_lock(ring.submit_q.submit_lock) ) {
[47746a2]	402	__STATS__( false,
	403	io.submit_q.helped += 1;
	404	)
[e46c753]	405	return;
	406	}
[2fafe7e]	407	/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
	408	__STATS__( true,
	409	io.submit_q.leader += 1;
	410	)
	411	#else
	412	for() {
	413	yield();
	414
	415	if( try_lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2) ) {
	416	__STATS__( false,
	417	io.submit_q.leader += 1;
	418	)
	419	break;
	420	}
	421
	422	// If some one else collected our index, we are done
	423	#warning ABA problem
	424	if( ring.submit_q.ready[picked] != idx ) {
	425	__STATS__( false,
	426	io.submit_q.helped += 1;
	427	)
	428	return;
	429	}
[e46c753]	430
[47746a2]	431	__STATS__( false,
[2fafe7e]	432	io.submit_q.busy += 1;
[47746a2]	433	)
[e46c753]	434	}
[2fafe7e]	435	#endif
[e46c753]	436
	437	// We got the lock
[be36ec3]	438	// Collect the submissions
[e46c753]	439	unsigned to_submit = __collect_submitions( ring );
	440
[be36ec3]	441	// Actually submit
	442	int ret = __io_uring_enter( ring, to_submit, false );
[309d814]	443
[2fafe7e]	444	#if defined(LEADER_LOCK)
	445	/* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
	446	next(ring.submit_q.submit_lock);
	447	#else
	448	unlock(ring.submit_q.submit_lock);
	449	#endif
[be36ec3]	450	if( ret < 0 ) return;
[e46c753]	451
	452	// Release the consumed SQEs
[34b61882]	453	__release_consumed_submission( ring );
[e46c753]	454
	455	// update statistics
[be36ec3]	456	__STATS__( false,
[47746a2]	457	io.submit_q.submit_avg.rdy += to_submit;
	458	io.submit_q.submit_avg.csm += ret;
	459	io.submit_q.submit_avg.cnt += 1;
	460	)
[e46c753]	461	}
[5dadc9b]	462	else {
	463	// get mutual exclusion
[2fafe7e]	464	#if defined(LEADER_LOCK)
	465	while(!try_lock(ring.submit_q.submit_lock));
	466	#else
	467	lock(ring.submit_q.submit_lock __cfaabi_dbg_ctx2);
	468	#endif
[2489d31]	469
[20ab637]	470	/* paranoid */ verifyf( ring.submit_q.sqes[ idx ].user_data != 0,
	471	/* paranoid */ "index %u already reclaimed\n"
	472	/* paranoid */ "head %u, prev %u, tail %u\n"
	473	/* paranoid */ "[-0: %u,-1: %u,-2: %u,-3: %u]\n",
	474	/* paranoid */ idx,
	475	/* paranoid / ring.submit_q.head, ring.submit_q.prev_head, *tail
	476	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 0) & (*ring.submit_q.mask) ]
	477	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 1) & (*ring.submit_q.mask) ]
	478	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 2) & (*ring.submit_q.mask) ]
	479	/* paranoid / ,ring.submit_q.array[ ((ring.submit_q.head) - 3) & (*ring.submit_q.mask) ]
	480	/* paranoid */ );
	481
[5dadc9b]	482	// Append to the list of ready entries
	483
	484	/* paranoid */ verify( idx <= mask );
[20ab637]	485	ring.submit_q.array[ (*tail) & mask ] = idx;
[5dadc9b]	486	__atomic_fetch_add(tail, 1ul32, __ATOMIC_SEQ_CST);
[d384787]	487
[5dadc9b]	488	// Submit however, many entries need to be submitted
[f00b26d4]	489	int ret = __io_uring_enter( ring, 1, false );
[5dadc9b]	490	if( ret < 0 ) {
	491	switch((int)errno) {
	492	default:
	493	abort( "KERNEL ERROR: IO_URING SUBMIT - %s\n", strerror(errno) );
	494	}
	495	}
[d384787]	496
[5dadc9b]	497	// update statistics
[47746a2]	498	__STATS__( false,
	499	io.submit_q.submit_avg.csm += 1;
	500	io.submit_q.submit_avg.cnt += 1;
	501	)
[5dadc9b]	502
[34b61882]	503	// Release the consumed SQEs
	504	__release_consumed_submission( ring );
[7bfc849]	505
[2fafe7e]	506	#if defined(LEADER_LOCK)
	507	next(ring.submit_q.submit_lock);
	508	#else
	509	unlock(ring.submit_q.submit_lock);
	510	#endif
[dd4e2d7]	511
	512	__cfadbg_print_safe( io, "Kernel I/O : Performed io_submit for %p, returned %d\n", active_thread(), ret );
[5dadc9b]	513	}
[2489d31]	514	}
[e46c753]	515
	516	static unsigned __collect_submitions( struct __io_data & ring ) {
	517	/* paranoid */ verify( ring.submit_q.ready != 0p );
	518	/* paranoid */ verify( ring.submit_q.ready_cnt > 0 );
	519
	520	unsigned to_submit = 0;
[4998155]	521	__u32 tail = *ring.submit_q.tail;
	522	const __u32 mask = *ring.submit_q.mask;
[e46c753]	523
	524	// Go through the list of ready submissions
	525	for( i; ring.submit_q.ready_cnt ) {
	526	// replace any submission with the sentinel, to consume it.
[4998155]	527	__u32 idx = __atomic_exchange_n( &ring.submit_q.ready[i], -1ul32, __ATOMIC_RELAXED);
[e46c753]	528
	529	// If it was already the sentinel, then we are done
	530	if( idx == -1ul32 ) continue;
	531
	532	// If we got a real submission, append it to the list
	533	ring.submit_q.array[ (tail + to_submit) & mask ] = idx & mask;
	534	to_submit++;
	535	}
	536
	537	// Increment the tail based on how many we are ready to submit
	538	__atomic_fetch_add(ring.submit_q.tail, to_submit, __ATOMIC_SEQ_CST);
	539
	540	return to_submit;
	541	}
[34b61882]	542
[4998155]	543	static __u32 __release_consumed_submission( struct __io_data & ring ) {
	544	const __u32 smask = *ring.submit_q.mask;
[732b406]	545
	546	if( !try_lock(ring.submit_q.release_lock __cfaabi_dbg_ctx2) ) return 0;
[4998155]	547	__u32 chead = *ring.submit_q.head;
	548	__u32 phead = ring.submit_q.prev_head;
[34b61882]	549	ring.submit_q.prev_head = chead;
[732b406]	550	unlock(ring.submit_q.release_lock);
	551
[4998155]	552	__u32 count = chead - phead;
[34b61882]	553	for( i; count ) {
[4998155]	554	__u32 idx = ring.submit_q.array[ (phead + i) & smask ];
[34b61882]	555	ring.submit_q.sqes[ idx ].user_data = 0;
	556	}
	557	return count;
	558	}
[47746a2]	559	#endif

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