linux-kernel - Re: [RFC 1/2] printk: Enable platform to provide a early boot clock

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Message-ID: <ea92b4fb-a1c9-a961-b67e-7834e351d6e1@infradead.org>
Date:   Thu, 31 May 2018 10:22:53 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Feng Tang <feng.tang@...el.com>
Cc:     Petr Mladek <pmladek@...e.com>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        alek.du@...el.com
Subject: Re: [RFC 1/2] printk: Enable platform to provide a early boot clock

On 05/31/2018 12:18 AM, Andy Shevchenko wrote:
> On Wed, May 30, 2018 at 12:20 PM, Feng Tang <feng.tang@...el.com> wrote:
>> Currently printk timestamp mostly come from the sched_clock which
>> depends on the clock setup, so there are many kernel logs started
>> with "[    0.000000]   " before the clock is calibrated.
>>
>> This patch will provide an debug option for specific platform to
>> provide a early boot time clock, so that we can have time info in
>> kernel log much earlier, which can show the time info for the early
>> kernel boot, and make boottime tuning/optimization easier (boot time
>> is critical for phone/tablet and embedded devices).
>>
>> Capable platform only need to setup the "boot_printk_clock_fn"
>> which could return time in nano seconds.
>>
>> Together with a TSC patch on x86 system, we have easily captured
>> some early boottime killer like unwind_init() which takes about
>> 300ms in boot phase.
> 
>> +static u64 printk_clock(void)
>> +{
>> +       /* If platform provides early boot printk clock, then use it */
>> +       if (unlikely(system_state == SYSTEM_BOOTING && boot_printk_clock_fn))
>> +               return boot_printk_clock_fn();
>> +       else
>> +               return local_clock();
> 
> 'else' is redundant.

So it is.  Is this a style comment?
This shouldn't matter to a smart compiler, should it?

>> +}

thanks,
-- 
~Randy