[PATCH 8/9] io_uring: skip futile iopoll iterations

Pavel Begunkov
2021-04-13T02:03:12Z

The only way to get out of io_iopoll_getevents() and continue iterating
is to have empty iopoll_list, otherwise the main loop would just exit.
So, instead of the unlock on 8th time heuristic, do that based on
iopoll_list.

Also, as no one can add new requests to iopoll_list while
io_iopoll_check() hold uring_lock, it's useless to spin with the list
empty, return in that case.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index cc6a44533802..1111968bbe7f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2387,7 +2387,7 @@ static void io_iopoll_try_reap_events(struct io_ring_ctx *ctx)
static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
{
unsigned int nr_events = 0;
- int iters = 0, ret = 0;
+ int ret = 0;

/*
* We disallow the app entering submit/complete with polling, but we
@@ -2416,10 +2416,13 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
* forever, while the workqueue is stuck trying to acquire the
* very same mutex.
*/
- if (!(++iters & 7)) {
+ if (list_empty(&ctx->iopoll_list)) {
mutex_unlock(&ctx->uring_lock);
io_run_task_work();
mutex_lock(&ctx->uring_lock);
+
+ if (list_empty(&ctx->iopoll_list))
+ break;
}

ret = io_iopoll_getevents(ctx, &nr_events, min);
--
2.24.0