linux-kernel - [QUESTION] Performance deterioration caused by commit 85f726a35e504418

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Message-ID: <992d3b1c-70db-5cc7-8400-39caa5d502d5@huawei.com>
Date:   Mon, 18 Oct 2021 11:23:14 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     <tom.zanussi@...ux.intel.com>, Steven Rostedt <rostedt@...dmis.org>
CC:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: [QUESTION] Performance deterioration caused by commit
 85f726a35e504418

Hi Tom and Steven,

commit 85f726a35e504418 use strncpy instead of memcpy when copying comm,
on ARM64 machine, this commit causes performance degradation.

I test the number of instructions executed by invoking the 
trace_sched_switch function once on an arm64 machine:
1. Use memcpy, the number of instructions executed is 850.
2. Use strncpy, the number of instructions executed 1100.
That is, use strncpy is almost 250 more instructions than memcpy.

Has the impact on performance been considered in this commit? :)
What is the impact of revert the patch?

Kind regards,
Jihong