linux-kernel - Re: [PATCH v2 3/3] alloc_tag: uninline code gated by mem_alloc_profiling

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Message-ID: <uz6j7wba2gk2wfn6foxs7v3wqdi5kwqnbolcdp3g7kzkw53a56@t7cyo3nyp2oa>
Date: Mon, 3 Feb 2025 16:46:52 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev, vbabka@...e.cz, 
	rostedt@...dmis.org, peterz@...radead.org, yuzhao@...gle.com, minchan@...gle.com, 
	souravpanda@...gle.com, pasha.tatashin@...een.com, 00107082@....com, 
	quic_zhenhuah@...cinc.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] alloc_tag: uninline code gated by
 mem_alloc_profiling_key in page allocator

On Sat, Feb 01, 2025 at 03:18:02PM -0800, Suren Baghdasaryan wrote:
> When a sizable code section is protected by a disabled static key, that
> code gets into the instruction cache even though it's not executed and
> consumes the cache, increasing cache misses. This can be remedied by
> moving such code into a separate uninlined function.
> On a Pixel6 phone, page allocation profiling overhead measured with
> CONFIG_MEM_ALLOC_PROFILING=y and profiling disabled is:
> 
>              baseline             modified
> Big core     4.93%                1.53%
> Medium core  4.39%                1.41%
> Little core  1.02%                0.36%
> 
> This improvement comes at the expense of the configuration when profiling
> gets enabled, since there is now an additional function call. The overhead
> from this additional call on Pixel6 is:
> 
> Big core     0.24%
> Middle core  0.63%
> Little core  1.1%
> 
> However this is negligible when compared with the overall overhead of the
> memory allocation profiling when it is enabled.
> On x86 this patch does not make noticeable difference because the overhead
> with mem_alloc_profiling_key disabled is much lower (under 1%) to start
> with, so any improvement is less visible and hard to distinguish from the
> noise. The overhead from additional call when profiling is enabled is also
> within noise levels.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>

One question: Is there any plan to enable MEM_ALLOC_PROFILING by default
in future?