linux-kernel - Re: [PATCH RFC] x86: enforce inlining for atomics

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Date:	Mon, 20 Apr 2015 23:56:45 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH RFC] x86: enforce inlining for atomics

On Mon, Apr 20, 2015 at 11:27:11PM +0200, Hagen Paul Pfeifer wrote:
> During some code analysis I realized that atomic_add, atomic_sub and
> friends are not necessarily inlined AND that each function is defined
> multiple times:
> 
> atomic_inc:          544 duplicates
> atomic_dec:          215 duplicates
> atomic_dec_and_test: 107 duplicates
> atomic64_inc:         38 duplicates
> [...]
> 
> Each definition is exact equally, e.g.:
> 
> ffffffff813171b8 <atomic_add>:
> 55         push   %rbp
> 48 89 e5   mov    %rsp,%rbp
> f0 01 3e   lock add %edi,(%rsi)
> 5d         pop    %rbp
> c3         retq
> 
> In turn each definition has one or more callsites (sure):
> 
> ffffffff81317c78: e8 3b f5 ff ff  callq  ffffffff813171b8 <atomic_add>
> [...]
> ffffffff8131a062: e8 51 d1 ff ff  callq  ffffffff813171b8 <atomic_add>
> [...]
> ffffffff8131a190: e8 23 d0 ff ff  callq  ffffffff813171b8 <atomic_add>
> [...]

Hmm, that must be config-specific as doing

objdump -D vmlinux | grep -i "atomic_add"

here gives me only "drm_atomic_add_affected_connectors" matches.

It probably gets inlined here always...

Other than that, this patch should actually even show some speedup as
we're getting rid of the stack preparation and function call overhead.
Have you done any benchmarks with it?

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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