Re: [PATCH v2] io_uring: only wake up sq thread while current task is in io worker context

[Jens Axboe <axboe@kernel.dk>]

On 11/12/20 9:44 AM, Xiaoguang Wang wrote:
> If IORING_SETUP_SQPOLL is enabled, sqes are either handled in sq thread
> task context or in io worker task context. If current task context is sq
> thread, we don't need to check whether should wake up sq thread.
> 
> io_iopoll_req_issued() calls wq_has_sleeper(), which has smp_mb() memory
> barrier, before this patch, perf shows obvious overhead:
>   Samples: 481K of event 'cycles', Event count (approx.): 299807382878
>   Overhead  Comma  Shared Object     Symbol
>      3.69%  :9630  [kernel.vmlinux]  [k] io_issue_sqe
> 
> With this patch, perf shows:
>   Samples: 482K of event 'cycles', Event count (approx.): 299929547283
>   Overhead  Comma  Shared Object     Symbol
>      0.70%  :4015  [kernel.vmlinux]  [k] io_issue_sqe
> 
> It shows some obvious improvements.

Applied, thanks.

-- 
Jens Axboe