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io_uring: batch task_work 

Batching task work up is an important performance optimisation, as
task_work_add is expensive.

In order to keep the semantics replace the task_list with a fake node
while processing the old list, and then do a cmpxchg at the end to see if
there is more work.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220622134028.2013417-6-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dylan Yudaken 2022-06-22 06:40:25 -07:00 committed by Jens Axboe
parent 923d159247
commit 3a0c037b0e
1 changed files with 12 additions and 8 deletions
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20
io_uring/io_uring.c
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@ -986,11 +986,11 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx, bool *locked)
percpu_ref_put(&ctx->refs);
}
static void handle_tw_list(struct llist_node *node,
struct io_ring_ctx **ctx, bool *locked)
struct io_ring_ctx **ctx, bool *locked,
struct llist_node *last)
{
do {
while (node != last) {
struct llist_node *next = node->next;
struct io_kiocb *req = container_of(node, struct io_kiocb,
io_task_work.node);
@ -1006,7 +1006,7 @@ static void handle_tw_list(struct llist_node *node,
}
req->io_task_work.func(req, locked);
node = next;
} while (node);
}
}
/**
@ -1045,11 +1045,15 @@ void tctx_task_work(struct callback_head *cb)
struct io_ring_ctx *ctx = NULL;
struct io_uring_task *tctx = container_of(cb, struct io_uring_task,
task_work);
struct llist_node *node = llist_del_all(&tctx->task_list);
struct llist_node fake = {};
struct llist_node *node = io_llist_xchg(&tctx->task_list, &fake);
if (node) {
handle_tw_list(node, &ctx, &uring_locked);
cond_resched();
handle_tw_list(node, &ctx, &uring_locked, NULL);
node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);
while (node != &fake) {
node = io_llist_xchg(&tctx->task_list, &fake);
handle_tw_list(node, &ctx, &uring_locked, &fake);
node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);
}
ctx_flush_and_put(ctx, &uring_locked);