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io_uring: optimise deferred tw execution

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We needed fake nodes in __io_run_local_work() and to avoid unecessary wake
ups while the task already running task_works, but we don't need them
anymore since wake ups are protected by cq_waiting, which is always
cleared by the time we're executing deferred task_work items.

Note that because of loose sync around cq_waiting clearing
io_req_local_work_add() may wake the task more than once, but that's
fine and should be rare to not hurt perf.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8839534891f0a2f1076e78554a31ea7e099f7de5.1673274244.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2023-01-09 14:46:13 +00:00 committed by Jens Axboe
parent d80c0f00d0
commit c3f4d39ee4
1 changed files with 7 additions and 17 deletions
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24
io_uring/io_uring.c
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@ -1322,17 +1322,16 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
static int __io_run_local_work(struct io_ring_ctx *ctx, bool *locked)
{
struct llist_node *node;
struct llist_node fake;
struct llist_node *current_final = NULL;
unsigned int loops = 0;
int ret = 0;
unsigned int loops = 1;
if (WARN_ON_ONCE(ctx->submitter_task != current))
return -EEXIST;
node = io_llist_xchg(&ctx->work_llist, &fake);
if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
again:
while (node != current_final) {
node = io_llist_xchg(&ctx->work_llist, NULL);
while (node) {
struct llist_node *next = node->next;
struct io_kiocb *req = container_of(node, struct io_kiocb,
io_task_work.node);
@ -1341,23 +1340,14 @@ again:
ret++;
node = next;
}
loops++;
if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
node = io_llist_cmpxchg(&ctx->work_llist, &fake, NULL);
if (node != &fake) {
loops++;
current_final = &fake;
node = io_llist_xchg(&ctx->work_llist, &fake);
if (!llist_empty(&ctx->work_llist))
goto again;
}
if (*locked)
io_submit_flush_completions(ctx);
trace_io_uring_local_work_run(ctx, ret, loops);
return ret;
}
static inline int io_run_local_work_locked(struct io_ring_ctx *ctx)