linux-kernel - Re: [v3 1/2] sched/clock: interface to allow timestamps early in boot

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Date:   Mon, 14 Aug 2017 11:44:56 -0400
From:   Pasha Tatashin <pasha.tatashin@...cle.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de, hpa@...or.com
Subject: Re: [v3 1/2] sched/clock: interface to allow timestamps early in boot

Hi Dou,

Thank you for your comments:

>>  {
>>      x86_init.timers.timer_init();
>>      tsc_init();
>> +    tsc_early_fini();
> 
> tsc_early_fini() is defined in patch 2, I guess you may miss it
> when you split your patches.

Indeed, I will move it to patch 2.

>> +static DEFINE_STATIC_KEY_TRUE(__use_sched_clock_early);
>> +static bool __read_mostly sched_clock_early_running;
>> +
> 
> In my opinion, these two parameters are repetitive, I suggest remove
> one.
> 
> eg. remove sched_clock_early_running like below
> First, static DEFINE_STATIC_KEY_FALSE(__use_sched_clock_early);

We can't change the static branches before jump_label_init() is called, 
and we start early boot timestamps before that

This is why having two booleans is appropriate: one that can be changed 
early in boot, and another to patch the hotcode in order to keep good 
performance after boot.

I will update comment before __use_sched_clock_early explaining the 
reason why we need two of them.

Thank you,
Pasha