From mboxrd@z Thu Jan  1 00:00:00 1970
From: linus.walleij@linaro.org (Linus Walleij)
Date: Fri, 29 Apr 2011 23:53:52 +0200
Subject: [patch 00/16] arm: Replace arm sched_clock by clocksource based
	sched_clock
In-Reply-To: <alpine.LFD.2.02.1104291900290.3005@ionos>
References: <20110423205036.795894921@linutronix.de>
	<20110429094606.GA5126@n2100.arm.linux.org.uk>
	<alpine.LFD.2.02.1104291217120.3005@ionos>
	<20110429103208.GA2849@atomide.com>
	<alpine.LFD.2.02.1104291900290.3005@ionos>
Message-ID: <BANLkTi=Xymqw9H+aNPbYUWDs7w5HzmJVkw@mail.gmail.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

2011/4/29 Thomas Gleixner <tglx@linutronix.de>:
> On Fri, 29 Apr 2011, Tony Lindgren wrote:
>> What about PRINTK_TIME? I think that uses sched_clock right from the
>> start.
>
> Right, but where is the problem ? A few time stamps with jiffies
> resolution and then the finegrained ones.

Jonas ?berg has this pending patch that we call "boot time recorder".
What it does is basically start a free running timer before the
kernel is booted, e.g. in U-boot or even in the ROM of your
machine if you can.

If we need more finegrained sched_clock() before the
clocksource is up, a good approach would be to utilize
something like that for sched_clock up to that point, plus
it has the upside that [0.000000] is as close to electrical
power-on as possible.

Yours,
Linus Walleij