When SETUP_IOPOLL and SETUP_SQPOLL are both enabled, applications don't need
to do io completion events polling again, they can rely on io_sq_thread to do
polling work, which can reduce cpu usage and uring_lock contention.
I modify fio io_uring engine codes a bit to evaluate the performance:
static int fio_ioring_getevents(struct thread_data *td, unsigned int min,
continue;
}
- if (!o->sqpoll_thread) {
+ if (o->sqpoll_thread && o->hipri) {
r = io_uring_enter(ld, 0, actual_min,
IORING_ENTER_GETEVENTS);
if (r < 0) {
and use "fio -name=fiotest -filename=/dev/nvme0n1 -iodepth=$depth -thread
-rw=read -ioengine=io_uring -hipri=1 -sqthread_poll=1 -direct=1 -bs=4k
-size=10G -numjobs=1 -time_based -runtime=120"
original codes
--------------------------------------------------------------------
iodepth | 4 | 8 | 16 | 32 | 64
bw | 1133MB/s | 1519MB/s | 2090MB/s | 2710MB/s | 3012MB/s
fio cpu usage | 100% | 100% | 100% | 100% | 100%
--------------------------------------------------------------------
with patch
--------------------------------------------------------------------
iodepth | 4 | 8 | 16 | 32 | 64
bw | 1196MB/s | 1721MB/s | 2351MB/s | 2977MB/s | 3357MB/s
fio cpu usage | 63.8% | 74.4%% | 81.1% | 83.7% | 82.4%
--------------------------------------------------------------------
bw improve | 5.5% | 13.2% | 12.3% | 9.8% | 11.5%
--------------------------------------------------------------------
>From above test results, we can see that bw has above 5.5%~13%
improvement, and fio process's cpu usage also drops much. Note this
won't improve io_sq_thread's cpu usage when SETUP_IOPOLL|SETUP_SQPOLL
are both enabled, in this case, io_sq_thread always has 100% cpu usage.
I think this patch will be friendly to applications which will often use
io_uring_wait_cqe() or similar from liburing.
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
---
fs/io_uring.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6a595c1..9f56723 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1574,6 +1574,8 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
}
io_commit_cqring(ctx);
+ if (ctx->flags & IORING_SETUP_SQPOLL)
+ io_cqring_ev_posted(ctx);
io_free_req_many(ctx, &rb);
}
@@ -6637,7 +6639,14 @@ static unsigned long io_uring_nommu_get_unmapped_area(struct file *file,
min_complete = min(min_complete, ctx->cq_entries);
- if (ctx->flags & IORING_SETUP_IOPOLL) {
+ /*
+ * When SETUP_IOPOLL and SETUP_SQPOLL are both enabled, user
+ * space applications don't need to do io completion events
+ * polling again, they can rely on io_sq_thread to do polling
+ * work, which can reduce cpu usage and uring_lock contention.
+ */
+ if (ctx->flags & IORING_SETUP_IOPOLL &&
+ !(ctx->flags & IORING_SETUP_SQPOLL)) {
ret = io_iopoll_check(ctx, &nr_events, min_complete);
} else {
ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
--
1.8.3.1
