linux-kernel - Re: [PATCH 0/2] optimise iov

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Message-ID: <bbaaf6fe-d456-a3b1-9f95-005e182eadfd@gmail.com>
Date:   Thu, 19 Nov 2020 18:02:44 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] optimise iov_iter

On 19/11/2020 17:20, Jens Axboe wrote:
> On 11/19/20 10:14 AM, Pavel Begunkov wrote:
>> On 19/11/2020 16:46, Jens Axboe wrote:
>>> On 11/19/20 8:29 AM, Pavel Begunkov wrote:
>>>> The first patch optimises iov_iter_npages() for the bvec case, and the
>>>> second helps code generation to kill unreachable code.
>>>>
>>>> Pavel Begunkov (2):
>>>>   iov_iter: optimise iov_iter_npages for bvec
>>>>   iov_iter: optimise iter type checking
>>>>
>>>>  include/linux/uio.h | 10 +++++-----
>>>>  lib/iov_iter.c      | 10 +++++-----
>>>>  2 files changed, 10 insertions(+), 10 deletions(-)
>>>
>>> Nice! Tested this and confirmed both the better code generation,
>>> and reduction in overhead in iov_iter_npages().
>>
>> Thanks! Did you find t-put/etc. boost with your setup?
> 
> Yeah, for this kind of test, if we shave 1% off the stack overhead,
> that directly yields an increase in peak IOPS. My numbers were close
> to yours, dropped about 1% of system overhead.

That's great. I was guessing how much of it can be due
to not cached bvec and was just tossed to somewhere else.

-- 
Pavel Begunkov