Messages in this thread | | | Date | Sun, 25 May 2008 17:30:13 +0300 | From | Pekka Paalanen <> | Subject | Re: Fwd: [PATCH] kmemcheck: SMP support |
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On Fri, 23 May 2008 16:19:43 +0200 "Vegard Nossum" <vegard.nossum@gmail.com> wrote:
> Oops, forgot to put you on Cc. I thought you might find this > interesting as well... :-)
Yes, thanks. My opinion is that mmiotrace can live well enough with runtime-disabling extra cpus when tracing starts. Multi-cpu effects to hardware access are not really in the focus but seeing the access in the first place. I'd rather wait to see if the per-cpu page table feature starts to evolve.
I quickly read through your code and tried to come up with race scenarios, but failed. Ok, one question which might be far fetched: is there a window for things to go wrong, when one cpu has faulted and is submitting the NMI, but another cpu is managing cpus' online state at the time? Is there a place in the cpu state management that might fault at a point where cpu maps are inconsistent? I doubt, but I don't know. And of course this could be a problem only when something is bringing cpus on- or offline.
Btw. isn't reserving a cpumask_t variable from the stack discouraged because it might have to deal with thousands of cpus and consume a lot of memory?
Thanks.
> ---------- Forwarded message ---------- > From: Vegard Nossum <vegard.nossum@gmail.com> > Date: Fri, May 23, 2008 at 4:17 PM > Subject: [PATCH] kmemcheck: SMP support > To: Ingo Molnar <mingo@elte.hu>, Pekka Enberg <penberg@cs.helsinki.fi> > Cc: linux-kernel@vger.kernel.org > > > Hi, > > This works on real hw, but not on qemu. It seems to get stuck waiting for one > of the atomic values to change. Don't know why yet, it might just be yet > another bug in qemu... (we've hit at least two of them so far. And they were > real bugs too.) > > But do you think this approach is feasible? It will kill interactivity, > that's for sure, though only when kmemcheck is run-time enabled and number > of CPUs > 1 (the more the worse). >
-- Pekka Paalanen http://www.iki.fi/pq/
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