[PATCH v2 2/3] io_uring: batch getting pcpu references

Pavel Begunkov
2019-12-21T16:16:02Z

percpu_ref_tryget() has its own overhead. Instead getting a reference
for each request, grab a bunch once per io_submit_sqes().

basic benchmark with submit and wait 128 non-linked nops showed ~5%
performance gain. (7044 KIOPS vs 7423)

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 513f1922ce6a..5392134f042f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1045,9 +1045,6 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
struct io_kiocb *req;

- if (!percpu_ref_tryget(&ctx->refs))
- return NULL;
-
if (!state) {
req = kmem_cache_alloc(req_cachep, gfp);
if (unlikely(!req))
@@ -4391,6 +4388,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
struct io_submit_state state, *statep = NULL;
struct io_kiocb *link = NULL;
int i, submitted = 0;
+ unsigned int extra_refs;
bool mm_fault = false;

/* if we have a backlog and couldn't flush it all, return BUSY */
@@ -4400,6 +4398,10 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
return -EBUSY;
}

+ if (!percpu_ref_tryget_many(&ctx->refs, nr))
+ return -EAGAIN;
+ extra_refs = nr;
+
if (nr > IO_PLUG_THRESHOLD) {
io_submit_state_start(&state, nr);
statep = &state;
@@ -4415,6 +4417,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
submitted = -EAGAIN;
break;
}
+ --extra_refs;
if (!io_get_sqring(ctx, req, &sqe)) {
__io_free_req(req);
break;
@@ -4451,6 +4454,8 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
io_queue_link_head(link);
if (statep)
io_submit_state_end(&state);
+ if (extra_refs)
+ percpu_ref_put_many(&ctx->refs, extra_refs);

/* Commit SQ ring head once we've consumed and submitted all SQEs */
io_commit_sqring(ctx);
--
2.24.0