linux-kernel - Re: [PATCH] stopmachine: add stopmachine

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Message-Id: <200807161115.55214.borntraeger@de.ibm.com>
Date:	Wed, 16 Jul 2008 11:15:55 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Max Krasnyansky <maxk@...lcomm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Zachary Amsden <zach@...are.com>
Subject: Re: [PATCH] stopmachine: add stopmachine_timeout

Am Dienstag, 15. Juli 2008 schrieb Rusty Russell:
> > btw Rusty, I just had this "why didn't I think of that" moments. This is
> > actually another way of handling my workload. I mean it certainly does not
> > fix the root case of the problems and we still need other things that we
> > talked about (non-blocking module delete, lock-free module insertion, etc)
> > but at least in the mean time it avoids wedging the machines for good.
> > btw I'd like that timeout in milliseconds. I think 5 seconds is way tooooo
> > long :).
> 
> We can make it ms, sure.  200ms should be plenty of time: worst I ever saw 
was 
> 150ms, and that was some weird Power box doing crazy stuff.  I wouldn't be 
> surprised if you'd never see 1ms on your hardware.

I disagree that 5 seconds is to long :-). I even think having it default to 0 
is the safest option for virtualized environments. What if the host is paging 
like hell and the vcpu cannot run due to a missing page? In that case 200ms 
can be an incredible short amount of time. If the timeout triggers, 
stop_machine_run fails, but everything would work fine - it just takes 
longer.

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