Re: [PATCH v2 3/3] alloc_tag: uninline code gated by mem_alloc_profiling_key in page allocator

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Feb 3, 2025 at 4:47 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> 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@google.com>
>
> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
>
> One question: Is there any plan to enable MEM_ALLOC_PROFILING by default
> in future?

It's left up to each distribution. In Android Common Kernel we are
enabling it with CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n and
allow vendors to enable it using kernel command line parameters.

>