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

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Date:   Sun, 1 May 2022 14:30:57 +0800
From:   Hao Xu <haoxu.linux@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, 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 4/30/22 21:11, Jens Axboe wrote:
> 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?
Sorry, I transposed 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.
Sure, put that in the Patch 7/9, I'll move it to the cover letter as
well.
> 
>> things to be done:
>>   - Still need some thinking about the work cancellation
> 
> Can you expand? What are the challenges with fixed workers and
> cancelation?
Currently, when a fixed worker fetch all the works from its private work
list, I use a temporary acct struct to hold them. This means at that
moment the cancellation cannot find these works which are going to run
but not in the private work list already. This won't be a big problem,
another acct member in io_worker{} should be good enough to resolve
that.
> 
>>   - 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.
>