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io_uring: optimise io_cqring_wait() hot path

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Turns out we always init struct io_wait_queue in io_cqring_wait(), even
if it's not used after, i.e. there are already enough of CQEs. And often
it's exactly what happens, for instance, requests may have been
completed inline, or in case of io_uring_enter(submit=N, wait=1).

It shows up in my profiler, so optimise it by delaying the struct init.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/6f1b81c60b947d165583dc333947869c3d85d037.1628471125.git.asml.silence@gmail.com
[axboe: fixed up for new cqring wait]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-08-09 09:07:32 -06:00 committed by Jens Axboe
parent 282cdc8693
commit 90291099f2
1 changed files with 6 additions and 8 deletions
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14
fs/io_uring.c
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@ -7063,14 +7063,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
const sigset_t __user *sig, size_t sigsz,
struct __kernel_timespec __user *uts)
{
struct io_wait_queue iowq = {
.wq = {
.private = current,
.func = io_wake_function,
.entry = LIST_HEAD_INIT(iowq.wq.entry),
},
.ctx = ctx,
};
struct io_wait_queue iowq;
struct io_rings *rings = ctx->rings;
signed long timeout = MAX_SCHEDULE_TIMEOUT;
int ret;
@ -7104,8 +7097,13 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
timeout = timespec64_to_jiffies(&ts);
}
init_waitqueue_func_entry(&iowq.wq, io_wake_function);
iowq.wq.private = current;
INIT_LIST_HEAD(&iowq.wq.entry);
iowq.ctx = ctx;
iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
iowq.cq_tail = READ_ONCE(ctx->rings->cq.head) + min_events;
trace_io_uring_cqring_wait(ctx, min_events);
do {
/* if we can't even flush overflow, don't wait for more */