[clocksource] jiffies as clocksource kills box

[clocksource] jiffies as clocksource kills box

[Mike Galbraith]

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Greetings,

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.

config attached

	-Mike

(I don't miss it, stumbled across while rummaging elsewhere...)


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Re: [clocksource] jiffies as clocksource kills box

[Thomas Gleixner]

On Tue, 15 Jan 2008, Mike Galbraith wrote:

> Greetings,
> 
> 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

Re: [clocksource] jiffies as clocksource kills box

[devzero]

>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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