Re: [PATCH] loop: inherit the ioprio in loop woker thread

[yunlong xing]

Bart Van Assche <bvanassche@xxxxxxx> 于2024年5月23日周四 02:12写道：
>
> On 5/22/24 10:57, Jens Axboe wrote:
> > On 5/22/24 11:38 AM, Bart Van Assche wrote:
> >> On 5/22/24 00:48, Yunlong Xing wrote:
> >>> @@ -1913,6 +1921,10 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
> >>>            set_active_memcg(old_memcg);
> >>>            css_put(cmd_memcg_css);
> >>>        }
> >>> +
> >>> +    if (ori_ioprio != cmd_ioprio)
> >>> +        set_task_ioprio(current, ori_ioprio);
> >>> +
> >>>     failed:
> >>>        /* complete non-aio request */
> >>>        if (!use_aio || ret) {
> >>
> >> Does adding this call in the hot path have a measurable performance impact?
> >
> > It's loop, I would not be concerned with overhead. But it does look pretty
> > bogus to modify the task ioprio from here.
>
> Hi Jens,
>
> Maybe Yunlong uses that call to pass the I/O priority to the I/O submitter?
>
> I think that it is easy to pass the I/O priority to the kiocb submitted by
> lo_rw_aio() without calling set_task_ioprio().
>
> lo_read_simple() and lo_write_simple() however call vfs_iter_read() /
> vfs_iter_write(). This results in a call of do_iter_readv_writev() and
> init_sync_kiocb(). The latter function calls get_current_ioprio(). This is
> probably why the set_task_ioprio() call has been added?

Yeah that's why I call set_task_ioprio.  I want to the loop kwoker task，submit
I/O to the real disk device，can pass the iopriority of the loop device request，
both lo_rw_aio() and lo_read_simple()/lo_write_simple().

Thanks,
yunlong.

>
> Thanks,
>
> Bart.
>
>