linux-kernel - Re: [PATCH RFC net-next v1] page_pool: import Jesper's page

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Message-ID: <4bb08c33-eac5-46e1-8d59-acc125946654@kernel.org>
Date: Mon, 24 Mar 2025 23:11:22 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Mina Almasry <almasrymina@...gle.com>,
 Toke Høiland-Jørgensen <toke@...e.dk>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>,
 Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH RFC net-next v1] page_pool: import Jesper's page_pool
 benchmark



On 24/03/2025 21.23, Mina Almasry wrote:
> On Mon, Mar 10, 2025 at 2:15 AM Toke Høiland-Jørgensen <toke@...e.dk> wrote:
>>
>> Mina Almasry <almasrymina@...gle.com> writes:
>>
>>> From: Jesper Dangaard Brouer <hawk@...nel.org>
>>>
>>> We frequently consult with Jesper's out-of-tree page_pool benchmark to
>>> evaluate page_pool changes.
>>>
>>> Consider importing the benchmark into the upstream linux kernel tree so
>>> that (a) we're all running the same version, (b) pave the way for shared
>>> improvements, and (c) maybe one day integrate it with nipa, if possible.
>>>
>>> I imported the bench_page_pool_simple from commit 35b1716d0c30 ("Add
>>> page_bench06_walk_all"), from this repository:
>>> https://github.com/netoptimizer/prototype-kernel.git
>>>
>>> I imported the benchmark, largely as-is. I only fixed build or
>>> checkpatch issues.
>>>
>>> Cc: Jesper Dangaard Brouer <hawk@...nel.org>
>>> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
>>> Cc: Jakub Kicinski <kuba@...nel.org>
>>> Cc: Toke Høiland-Jørgensen <toke@...e.dk>
>>> Cc: netdev@...r.kernel.org
>>> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>>>
>>> ---
>>>
>>> RFC discussion points:
>>> - Desirable to import it?
>>
>> I think so, yeah.
>>
>>> - Can the benchmark be imported as-is for an initial version? Or needs
>>>    lots of modifications?
>>
>> One thing that I was discussing with Jesper the other day is that the
>> current version allocates the page_pool itself in softirq context, which
>> leads to some "may sleep" warning. I think we should fix that before
>> upstreaming.
>>
> 
> I don't think I saw that warning for whatever reason. Do you by any
> chance have a fix that I can squash? Or do you think it is very
> critical to fix this before upstreaming? I.e. not follow up with a
> fix?

The tasklet trick in the benchmark module is to fake that code is
running in softirq context, which avoids taking the _bh lock variants.

In the past the performance was really different between the two
execution contexts, but in all of my recent experiments [1][2], the
performance differences are gone. So, I think we can simply drop the
ugly tasklet setup tricks.

  [1] 
https://github.com/xdp-project/xdp-project/blob/main/areas/mem/page_pool07_bench_DMA_fix.org
  [2] 
https://github.com/xdp-project/xdp-project/blob/main/areas/mem/page_pool08_bench_AMD.org

BTW it is awesome that you are pushing this to get upstreamed.

--Jesper