linux-kernel - Re: [PATCH V1 Resend 4/5] tick-sched: don't call update_wall_time() when delta is lesser than tick

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Date:	Tue, 15 Apr 2014 20:44:45 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
cc:	linaro-kernel@...ts.linaro.org,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arvind.Chauhan@....com, linaro-networking@...aro.org,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH V1 Resend 4/5] tick-sched: don't call update_wall_time()
 when delta is lesser than tick_period



On Tue, 15 Apr 2014, Viresh Kumar wrote:

> In tick_do_update_jiffies64() we are processing ticks only if delta is greater
> than tick_period. This is what we are supposed to do here and it broke a bit
> with this patch:
> 
> commit 47a1b796306356f358e515149d86baf0cc6bf007
> Author: John Stultz <john.stultz@...aro.org>
> Date:   Thu Dec 12 13:10:55 2013 -0800
> 
>     tick/timekeeping: Call update_wall_time outside the jiffies lock

Please look how I massaged the change log. There is no point in
copying the whole gunk.
 
> With above patch, we might end up calling update_wall_time() even if delta is
> found to be smaller that tick_period. Fix this by reversing the check and
> returning early.

Well.

> Cc: <stable@...r.kernel.org> # v3.14+
> Cc: John Stultz <john.stultz@...aro.org>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  kernel/time/tick-sched.c | 32 +++++++++++++++++---------------
>  1 file changed, 17 insertions(+), 15 deletions(-)

That's not how we do bug fixes if they can be done with 3 lines of
change. See the commit.

Thanks,

	tglx


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