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

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Message-Id: <200807141351.25092.borntraeger@de.ibm.com>
Date:	Mon, 14 Jul 2008 13:51:25 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH] stopmachine: add stopmachine_timeout

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. 

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?
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