linux-kernel - Re: [PATCH] Fix clock_gettime vsyscall time warp

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Message-ID: <20091117095955.0df508a5@mschwide.boeblingen.de.ibm.com>
Date:	Tue, 17 Nov 2009 09:59:55 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	tglx@...utronix.de, mingo@...e.hu,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix clock_gettime vsyscall time warp

On Tue, 17 Nov 2009 13:49:50 +0800
Lin Ming <ming.m.lin@...el.com> wrote:

> The root cause is the NTP adjusted clock multiplier(timekeeper.mult) is
> not updated to vsyscall gtod data(vsyscall_gtod_data.clock.mult). 
> 
> Since commit 0a544198 "timekeeping: Move NTP adjusted clock multiplier
> to struct timekeeper", clock->mult is only the unmodified multiplier.
> 
> Below patch passes the adjusted clock multiplier to update_vsyscall.
> -void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
> +void update_vsyscall(struct timespec *wall_time, struct clocksource *clock, u32 mult)
> 
> With this patch applied to 2.6.32-rc7, I have been running
> time-warp-test for many hours without any time warp on both x86_64 and
> ia64 machines.
> 
> This patch also touches the powerpc code, so it would be very
> appreciated if anyone can help to test it on powerpc.

Ouch! Yes, good catch. That patch needs to go into 2.6.32.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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