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

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Date:	Mon, 14 Jul 2008 22:34:40 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	virtualization@...ts.linux-foundation.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zachary Amsden <zach@...are.com>
Subject: Re: [PATCH] stopmachine: add stopmachine_timeout

On Monday 14 July 2008 21:51:25 Christian Borntraeger wrote:
> Am Montag, 14. Juli 2008 schrieb Hidetoshi Seto:
> > +	/* Wait all others come to life */
> > +	while (cpus_weight(prepared_cpus) != num_online_cpus() - 1) {
> > +		if (time_is_before_jiffies(limit))
> > +			goto timeout;
> > +		cpu_relax();
> > +	}
> > +
>
> Hmm. I think this could become interesting on virtual machines. The
> hypervisor might be to busy to schedule a specific cpu at certain load
> scenarios. This would cause a failure even if the cpu is not really locked
> up. We had similar problems with the soft lockup daemon on s390.

5 seconds is a fairly long time.  If all else fails we could have a config 
option to simply disable this code.

> It would be good to not-use wall-clock time, but really used cpu time
> instead. Unfortunately I have no idea, if that is possible in a generic
> way. Heiko, any ideas?

Ah, cpu time comes up again.  Perhaps we should actually dig that up again; 
Zach and Jeremy CC'd.

Thanks,
Rusty.
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