linux-kernel - Re: [RFC v3 0/9] fixed worker

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Date:   Sat, 30 Apr 2022 07:11:56 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Hao Xu <haoxu.linux@...il.com>, io-uring@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v3 0/9] fixed worker

On 4/29/22 4:18 AM, Hao Xu wrote:
> This is the third version of fixed worker implementation.
> Wrote a nop test program to test it, 3 fixed-workers VS 3 normal workers.
> normal workers:
> ./run_nop_wqe.sh nop_wqe_normal 200000 100 3 1-3
>         time spent: 10464397 usecs      IOPS: 1911242
>         time spent: 9610976 usecs       IOPS: 2080954
>         time spent: 9807361 usecs       IOPS: 2039284
> 
> fixed workers:
> ./run_nop_wqe.sh nop_wqe_fixed 200000 100 3 1-3
>         time spent: 17314274 usecs      IOPS: 1155116
>         time spent: 17016942 usecs      IOPS: 1175299
>         time spent: 17908684 usecs      IOPS: 1116776

I saw these numbers in v2 as well, and I have to admit I don't
understand them. Because on the surface, it sure looks like the first
set of results (labeled "normal") are better than the second "fixed"
set. Am I reading them wrong, or did you transpose them?

I think this patch series would benefit from a higher level description
of what fixed workers mean in this context. How are they different from
the existing workers, and why would it improve things.

> things to be done:
>  - Still need some thinking about the work cancellation

Can you expand? What are the challenges with fixed workers and
cancelation?

>  - not very sure IO_WORKER_F_EXIT is safe enough on synchronization
>  - the iowq hash stuff is not compatible with fixed worker for now

We might need to extract the hashing out a bit so it's not as tied to
the existing implementation.

-- 
Jens Axboe