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

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Date:   Sat, 11 Sep 2021 16:33:52 +0200
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 2/2] scripts: ftrace - move the nop-processing in
 ftrace_init to compile time

On Sat, Sep 11, 2021 at 09:50:43PM +0800, Yinan Liu wrote:
> When ftrace is enabled, ftrace_init will consume a period of
> time, usually around 15~20ms. Approximately 60% of the time is
> consumed by nop-processing. Moving the nop-processing to the
> compile time can speed up the kernel boot process.
> 
> performance test:
>         env:    Intel(R) Xeon(R) CPU E5-2682 v4 @ 2.50GHz

If you use objtool's -M argument instead of recordmcount, you already
get this and you can avoid running recordmcount entirely.