linux-kernel - Re: [PATCH] Add sched_clock to AT91 TCB clocksource driver

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Message-ID: <CANqCtQLuvFSsL3N3HdxdhnmO=2g4qsUTPX5rym1FUH1Lo8-ofA@mail.gmail.com>
Date:	Mon, 1 Aug 2011 22:00:00 +0200
From:	Remy Bohmer <linux@...mer.net>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Remy Bohmer <l.pinguin@...il.com>, Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Add sched_clock to AT91 TCB clocksource driver

Hi,

>> But late_time_init does it before the sched_clock is declared stable.
>> Until that point sched_clock will always return zero, as such we can
>> IMHO safely assume that the scheduler is designed such that it can
>> handle fixed zero timestamps for a while.
>
> You're confused.
>
> If you provide your own sched_clock(), that's what is used by everyone
> who calls sched_clock() both before and after sched_clock_init() has
> been called.
>
> sched_clock_cpu() and cpu_clock() both will return zero up until
> sched_clock_init() has been called, but sched_clock() itself may not.
>
> And these parts of the scheduler I'm talking about use sched_clock()
> itself, not sched_clock_cpu() nor cpu_clock().

Yep. You are right. I was confused... Sorry.

Kind regards,

Remy
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