linux-kernel - Re: [RFC PATCH 0/1] Large folios in block buffered IO path

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Message-ID: <f6878438-8fcf-4f78-88f5-e7f275b157eb@amd.com>
Date: Fri, 29 Nov 2024 16:02:19 +0530
From: Bharata B Rao <bharata@....com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, nikunj@....com, vbabka@...e.cz, david@...hat.com,
 akpm@...ux-foundation.org, yuzhao@...gle.com, axboe@...nel.dk,
 viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
 joshdon@...gle.com, clm@...a.com
Subject: Re: [RFC PATCH 0/1] Large folios in block buffered IO path

On 29-Nov-24 5:01 AM, Mateusz Guzik wrote:
> On Thu, Nov 28, 2024 at 12:24 PM Bharata B Rao <bharata@....com> wrote:
>>
>> On 28-Nov-24 10:07 AM, Bharata B Rao wrote:
>>> On 28-Nov-24 9:52 AM, Matthew Wilcox wrote:
>>>> On Thu, Nov 28, 2024 at 09:31:50AM +0530, Bharata B Rao wrote:
>>>>> However a point of concern is that FIO bandwidth comes down drastically
>>>>> after the change.
>>>>>
>>>>>          default                inode_lock-fix
>>>>> rw=30%
>>>>> Instance 1    r=55.7GiB/s,w=23.9GiB/s        r=9616MiB/s,w=4121MiB/s
>>>>> Instance 2    r=38.5GiB/s,w=16.5GiB/s        r=8482MiB/s,w=3635MiB/s
>>>>> Instance 3    r=37.5GiB/s,w=16.1GiB/s        r=8609MiB/s,w=3690MiB/s
>>>>> Instance 4    r=37.4GiB/s,w=16.0GiB/s        r=8486MiB/s,w=3637MiB/s
>>>>
>>>> Something this dramatic usually only happens when you enable a debugging
>>>> option.  Can you recheck that you're running both A and B with the same
>>>> debugging options both compiled in, and enabled?
>>>
>>> It is the same kernel tree with and w/o Mateusz's inode_lock changes to
>>> block/fops.c. I see the config remains same for both the builds.
>>>
>>> Let me get a run for both base and patched case w/o running perf lock
>>> contention to check if that makes a difference.
>>
>> Without perf lock contention
>>
>>                   default                         inode_lock-fix
>> rw=30%
>> Instance 1      r=54.6GiB/s,w=23.4GiB/s         r=11.4GiB/s,w=4992MiB/s
>> Instance 2      r=52.7GiB/s,w=22.6GiB/s         r=11.4GiB/s,w=4981MiB/s
>> Instance 3      r=53.3GiB/s,w=22.8GiB/s         r=12.7GiB/s,w=5575MiB/s
>> Instance 4      r=37.7GiB/s,w=16.2GiB/s         r=10.4GiB/s,w=4581MiB/s
>>
> 
> per my other e-mail can you follow willy's suggestion and increase the hash?

With Mateusz's inode_lock fix and PAGE_WAIT_TABLE_BITS value of 10, 14, 
16 and 20.
(Two values given with each instance below are FIO READ bw and WRITE bw)

                 10              14              16              20
rw=30%
Instance 1      11.3GiB/s       14.2GiB/s       14.8GiB/s       14.9GiB/s
                 4965MiB/s       6225MiB/s       6487MiB/s       6552MiB/s
Instance 2      12.3GiB/s       10.4GiB/s       10.9GiB/s       11.0GiB/s
                 5389MiB/s       4548MiB/s       4770MiB/s       4815MiB/s
Instance 3      11.1GiB/s       12.3GiB/s       11.2GiB/s       13.5GiB/s
                 4864MiB/s       5410MiB/s       4923MiB/s       5927MiB/s
Instance 4      12.3GiB/s       13.7GiB/s       13.0GiB/s       11.4GiB/s
                 5404MiB/s       6004MiB/s       5689MiB/s       5007MiB/s

Number of hash buckets don't seem to matter all that much in this case.

Regards,
Bharata.