linux-kernel - Re: [PATCH v5 1/2] io_uring: minor io_cqring

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Message-ID: <dc8bfa6b-5e3b-e2a9-b7b5-da5bbc70d3bc@kernel.dk>
Date:   Wed, 9 Mar 2022 16:43:15 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Olivier Langlois <olivier@...llion01.com>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     Hao Xu <haoxu@...ux.alibaba.com>,
        io-uring <io-uring@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] io_uring: minor io_cqring_wait() optimization

On 3/8/22 10:36 PM, Olivier Langlois wrote:
> On Tue, 2022-03-08 at 17:54 -0700, Jens Axboe wrote:
>> On 3/8/22 3:17 PM, Olivier Langlois wrote:
>>> Move up the block manipulating the sig variable to execute code
>>> that may encounter an error and exit first before continuing
>>> executing the rest of the function and avoid useless computations
>>
>> I don't think this is worthwhile doing. If you're hitting an error
>> in any of them, it's by definition not the fast path.
>>
> Well, by itself it is not a big improvement but it is still an
> improvement.
> 
> but most importantly, it has to be considered in the context of the
> current patchset because in patch #2, the following step is to
> 
> 1. acquire the napi spin lock
> 2. splice the context napi list into a local one.
> 3. release the lock
> 
> If this patch is not in place before patch #2, you would need undo all
> that before returning from the sig block which would make the function
> bigger when all that is completely avoidable by accepting this patch...
> 
> Both patches were together in v1 but I decided to break them apart
> thinking that this was the right thing to do...

Yeah ok, it does make sense in the context of patch 2. Thanks!

-- 
Jens Axboe