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Subject[PATCH 4/6] io_uring: separate DRAIN flushing into a cold path
Date
io_commit_cqring() assembly doesn't look good with extra code handling
drained requests. IOSQE_IO_DRAIN is slow and discouraged to be used in
a hot path, so try to minimise its impact by putting it into a helper
and doing a fast check.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 067ebdeb1ba4..acf6ce9eee68 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -982,19 +982,6 @@ static inline bool req_need_defer(struct io_kiocb *req)
return false;
}

-static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)
-{
- struct io_kiocb *req;
-
- req = list_first_entry_or_null(&ctx->defer_list, struct io_kiocb, list);
- if (req && !req_need_defer(req)) {
- list_del_init(&req->list);
- return req;
- }
-
- return NULL;
-}
-
static struct io_kiocb *io_get_timeout_req(struct io_ring_ctx *ctx)
{
struct io_kiocb *req;
@@ -1127,6 +1114,19 @@ static void io_kill_timeouts(struct io_ring_ctx *ctx)
spin_unlock_irq(&ctx->completion_lock);
}

+static void __io_queue_deferred(struct io_ring_ctx *ctx)
+{
+ do {
+ struct io_kiocb *req = list_first_entry(&ctx->defer_list,
+ struct io_kiocb, list);
+
+ if (req_need_defer(req))
+ break;
+ list_del_init(&req->list);
+ io_queue_async_work(req);
+ } while (!list_empty(&ctx->defer_list));
+}
+
static void io_commit_cqring(struct io_ring_ctx *ctx)
{
struct io_kiocb *req;
@@ -1136,8 +1136,8 @@ static void io_commit_cqring(struct io_ring_ctx *ctx)

__io_commit_cqring(ctx);

- while ((req = io_get_deferred_req(ctx)) != NULL)
- io_queue_async_work(req);
+ if (unlikely(!list_empty(&ctx->defer_list)))
+ __io_queue_deferred(ctx);
}

static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
--
2.24.0
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