linux-kernel - Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot

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Message-ID: <20170927144506.GU20805@n2100.armlinux.org.uk>
Date:   Wed, 27 Sep 2017 15:45:06 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        john.stultz@...aro.org, sboyd@...eaurora.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com
Subject: Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early
 in boot

On Wed, Aug 30, 2017 at 02:03:22PM -0400, Pavel Tatashin wrote:
> In Linux printk() can output timestamps next to every line.  This is very
> useful for tracking regressions, and finding places that can be optimized.
> However, the timestamps are available only later in boot. On smaller
> machines it is insignificant amount of time, but on larger it can be many
> seconds or even minutes into the boot process.

The sched_clock work I did for ARM could be setup really early at boot,
from setup_arch().  I tried to encourage platforms to do that, but all
my encouragement fell on deaf ears - most people setup the sched_clock
source along side the time initialisation on ARM.

I don't think we need yet another "early" mechanism to solve this problem,
we just need people to use the existing mechanism to register their
sched_clock implementation earlier.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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