On 11/22/2019 9:01 AM, Jackie Liu wrote:
> From: Jackie Liu <liuyun01@xxxxxxxxxx>
>
> We don't need to set drain_next every time, make a small judgment
> and add unlikely, it looks like there will be a little optimization.
>
Not sure about that. It's 1 CMP + 1 SETcc/STORE, which works pretty fast
as @drain_next is hot (especially after read) and there is no write-read
dependency close. For yours, there is likely always 3 CMPs in the way.
Did you benchmarked it somehow or compared assembly?
> Signed-off-by: Jackie Liu <liuyun01@xxxxxxxxxx>
> ---
> resend that patch, because reject by mail-list.
>
> fs/io_uring.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 013e5ed..f4ec44a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2938,12 +2938,14 @@ static void __io_queue_sqe(struct io_kiocb *req)
> static void io_queue_sqe(struct io_kiocb *req)
> {
> int ret;
> + bool drain_link = req->flags & REQ_F_DRAIN_LINK;
>
> - if (unlikely(req->ctx->drain_next)) {
> + if (unlikely(req->ctx->drain_next && !drain_link)) {
> req->flags |= REQ_F_IO_DRAIN;
> req->ctx->drain_next = false;
> + } else if (unlikely(drain_link)) {
> + req->ctx->drain_next = true;
> }
> - req->ctx->drain_next = (req->flags & REQ_F_DRAIN_LINK);
>
> ret = io_req_defer(req);
> if (ret) {
>
--
Pavel Begunkov
