lkml.org 
[lkml]   [2004]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/11] oprofile: arch-independent code for stack trace sampling
On Tue, Nov 09, 2004 at 10:35:48PM +1100, Greg Banks wrote:

> > oprofile is currently doing suspicious things with smp_processor_id() in
> > premptible reasons. Is this patch compounding things?
>
> It's not changing the contexts where smp_processor_id() is called,
> just pushing it down one level from a bunch of interrupt handlers
> to the 2 oprofile sampling functions they call. If it was busted
> before it's no more nor less busted now.
>
> I presume the perceived problem is that with CONFIG_PREEMPT=y the
> thread can be pre-empted onto another CPU? If it makes everyone
> happier I can sprinkle a few preempt_disable()s around, but I'd
> prefer to do it in a subsequent patch rather than respin this.

Andrew: basically the warning is false, there is no bug in this code.

we don't want to use preempt_disable(). Instead we want some way to get
a CPU ID and then carry on in pre-emptible fashion. It's only used to
index into an array, and if we get pre-empted onto another CPU it's not
a major deal.

(Yes, this breaks with CPU hotplug, but so does the rest of OProfile and
I've yet to see a sensible API for handling this, that is a ctor/dtor
style API)

regards
john
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:07    [from the cache]
©2003-2011 Jasper Spaans