Subject: Re: [v3 1/2] sched/clock: interface to allow timestamps early in boot
To: Dou Liyang <douly.fnst@cn.fujitsu.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, mingo@redhat.com, peterz@infradead.org,
        tglx@linutronix.de, hpa@zytor.com
References: <1502477455-314781-1-git-send-email-pasha.tatashin@oracle.com>
 <1502477455-314781-2-git-send-email-pasha.tatashin@oracle.com>
 <966f910e-f6be-f4df-2600-37133075dbde@cn.fujitsu.com>
From: Pasha Tatashin <pasha.tatashin@oracle.com>
Message-ID: <2043c873-1d94-8897-bbaa-bd1b82640652@oracle.com>
Date: Mon, 14 Aug 2017 11:44:56 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.1
MIME-Version: 1.0
In-Reply-To: <966f910e-f6be-f4df-2600-37133075dbde@cn.fujitsu.com>
Content-Type: text/plain; charset=gbk; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 998
Lines: 36

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