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

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Message-Id: <200807151810.00365.rusty@rustcorp.com.au>
Date:	Tue, 15 Jul 2008 18:09:59 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	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

On Tuesday 15 July 2008 12:24:54 Max Krasnyansky wrote:
> Heiko Carstens wrote:
> > On Mon, Jul 14, 2008 at 11:56:18AM -0700, Jeremy Fitzhardinge wrote:
> > This is asking for trouble... a config option to disable this would be
> > nice. But as I don't know which problem this patch originally addresses
> > it might be that this is needed anyway. So lets see why we need it first.
>
> How about this. We'll make this a sysctl, as Rusty already did, and set the
> default to 0 which means "never timeout". That way crazy people like me who
> care about this scenario can enable this feature.

Indeed, this was my thought too.  s390 can initialize it to zero somewhere in 
their boot code.

> 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.

The ipi idea would handle your case a little more nicely, too, but that's 
probably not going to hit this merge window.

Cheers,
Rusty.
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