lkml.org 
[lkml]   [2014]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] perf, x86: Fall back to vmalloc for BTS buffer allocation
On Wed, Sep 10, 2014 at 06:35:56PM +0200, Peter Zijlstra wrote:
> On Wed, Sep 10, 2014 at 04:40:12PM +0200, Andi Kleen wrote:
> > > We did this once, and that blew up big time.
> > >
> > > Even now, vmalloc_fault() has a very explicit:
> > >
> > > WARN_ON_ONCE(in_nmi());
> > >
> > > So this isn't going to happen until you fix that.
> >
> > Good point.
> >
> > We just need to call vmalloc_sync_all at allocation time,
> > no need to change vmalloc_fault.
>
> Somehow that wasn't considered adequate, but lemme try and dig out that
> thread. It should be somewhere...
>
> https://lkml.org/lkml/2010/7/14/465

Note that since then we have actually fixed the 'cannot fault from NMI
context' thing, so we should be able to actually take those faults. I
suspect we can simply remove those WARNs from the vmalloc fault path,
but it would need double checking to see if there's no other reasons.

Also:

https://lkml.org/lkml/2014/4/10/581
https://patchwork.kernel.org/patch/3048111/

I'm not entirely sure what the final conclusion is, except to note that
it didn't happen.


\
 
 \ /
  Last update: 2014-09-10 19:41    [W:0.080 / U:0.208 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site