linux-kernel - Re: [PATCH] groups: Use bsearch instead of hand rolled implementation

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Message-ID: <87jz63jmec.fsf@gmail.com>
Date: Mon, 26 May 2025 10:46:03 -0700
From: Collin Funk <collin.funk1@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] groups: Use bsearch instead of hand rolled implementation

Hi Al,

Al Viro <viro@...iv.linux.org.uk> writes:

> Careful - that really needs profiling with setups where processes have
> a bunch of supplementary groups.
>
> It *is* on hot paths, and while the current version will be inlined,
> yours will do a bunch of indirect calls.  These days that can be
> costly.

Sure, makes sense.

I would assume that gid_cmp/gid_lt/gid_gt all get inlined no matter
what, but I am not sure if the conversion to 'grp' to a void pointer for
the generic bsearch prevents some optimizations.

> Reducing code duplication is a good thing, but not when it creates
> measurable regressions...

Yes, that makes sense.

There is '__inline_bsearch', but I'll have to do some expirementing to
make sure that gets optimized well.

Thanks,
Collin