linux-kernel - Re: [clocksource] jiffies as clocksource kills box

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Date:	Sat, 02 Feb 2008 14:01:27 +0100
From:	devzero@....de
To:	tglx@...utronix.de
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [clocksource] jiffies as clocksource kills box

>I have a patch pending for the PIT issue. Will add jiffies to this as
>well.

yes, please. 
while trying to analyze a timer issue and learning about that timer stuff, i "killed" my box twice because i didn`t know that "echo jiffies|pit > current_clocksource" is a no-no with dynticks.
this happened with vendor kernel and thought i hit a bug, so i tried vanilla but.....same issue.

not a big one, but that patch would be a time-saver for those who don`t know...

roland


>> Per $subject, echo jiffies > current_clocksource pretty thoroughly kills
>> my P4 box, and does so with every kernel I have (2.6.22->present).  I
>> can drive the box via mouse clicks and poke around, but trying to select
>> another clocksource thereafter is nogo.. cat current_clocksource emits
>> jiffies, and box remains comatose unless prodded.
>
>I guess your box has high resolution timers and/or dynamic ticks
>enabled. In that case we really can not switch to jiffies. We also
>have to prevent PIT from being selected. 
>
>I have a patch pending for the PIT issue. Will add jiffies to this as
>well.
>
>We'll fix that in .25 as it requires root user interaction and does
>not show up magically.
>
>Thanks,
>	tglx
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