linux-kernel - Re: [PATCH 1/1] arm/syscalls: mark syscall invocation as

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Message-Id: <20250922121730.986761-1-pengcan@kylinos.cn>
Date: Mon, 22 Sep 2025 20:17:30 +0800
From: Can Peng <pengcan@...inos.cn>
To: catalin.marinas@....com,
	will@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] arm/syscalls: mark syscall invocation as

Hello,

>> The invoke_syscall() function is overwhelmingly called for
>> valid system call entries. Annotate the main path with likely()
>> to help the compiler generate better branch prediction hints,
>> reducing CPU pipeline stalls due to mispredictions.
>> 
>> This is a micro-optimization targeting syscall-heavy workloads.
>
>Does it actually make a measurable difference?

This change implements a micro-optimization. Benchmark results
from the Kunpeng 920 machine are as follows:

before:
- lat_syscall result 
write call      0.2332  0.2337  0.2341
read call       0.2501  0.2493  0.2506

after:
- lat_syscall result
write call      0.2301  0.2316  0.2307
read call       0.2492  0.2498  0.2491


Best regards,
Can Peng