linux-kernel - Re: [PATCH v2 2/2] scripts: ftrace - move the nop-processing in ftrace

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Date:   Tue, 16 Nov 2021 09:10:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yinan Liu <yinan@...ux.alibaba.com>
Cc:     rostedt@...dmis.org, mark-pk.tsai@...iatek.com, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] scripts: ftrace - move the nop-processing in
 ftrace_init to compile time

On Tue, Nov 16, 2021 at 10:49:42AM +0800, Yinan Liu wrote:
> In some business scenarios, GCC versions are so old that
> optimizations in ftrace cannot be completed, such as
> -mrecord-mcount and -mnop-mcount. The recordmCount in the
> kernel is actually used. In this case, ftrace_init will
> consume a period of time, usually around 9~12ms. Do nop
> substitution in recordmcount.c to speed up ftrace_init.

I really don't buy this.. if you can build a fresh kernel, you can
install a fresh gcc too -- and if you care about performance that's a
very good idea anyway.