Date: Wed, 27 Sep 2017 20:11:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, john.stultz@linaro.org,
        sboyd@codeaurora.org, x86@kernel.org, linux-kernel@vger.kernel.org,
        mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com,
        douly.fnst@cn.fujitsu.com
Subject: Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early
 in boot
Message-ID: <20170927181140.GN17526@worktop.programming.kicks-ass.net>
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 <1504116205-355281-2-git-send-email-pasha.tatashin@oracle.com>
 <20170927144506.GU20805@n2100.armlinux.org.uk>
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On Wed, Sep 27, 2017 at 03:45:06PM +0100, Russell King - ARM Linux wrote:
> 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.

x86 is a bit 'special' in the whole sched_clock department. But yes, we
should very much make the regular sched_clock() happen earlier.