linux-kernel - Re: [PATCH] sched: sched_clock() clocksource handling.

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Date:	Tue, 02 Jun 2009 04:49:26 -0700
From:	Daniel Walker <dwalker@...o99.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Walleij <linus.ml.walleij@...il.com>,
	Andrew Victor <linux@...im.org.za>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Stultz <johnstul@...ux.vnet.ibm.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: sched_clock() clocksource handling.

On Tue, 2009-06-02 at 16:54 +0900, Paul Mundt wrote:
>  unsigned long long __attribute__((weak)) sched_clock(void)
>  {
> -       return (unsigned long long)(jiffies - INITIAL_JIFFIES)
> -                                       * (NSEC_PER_SEC / HZ);
> +       unsigned long long time;
> +       struct clocksource *clock;
> +
> +       rcu_read_lock();
> +       clock = rcu_dereference(sched_clocksource);
> +       time = cyc2ns(clock, clocksource_read(clock));
> +       rcu_read_unlock();
> +
> +       return time;
>  }

My concerns with the locking here still stand. Nothing you've said or
done bolsters the clocksource in modules argument. I think what your
planning for sh clocksources seems very inelegant. I would imagine a
better solution is out there. I'd prefer if you just leave sched_clock
alone.

Daniel

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