lkml.org 
[lkml]   [2007]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu variables
On Tue, 27 Nov 2007 15:22:56 -0800 (PST)
Christoph Lameter <clameter@sgi.com> wrote:

> On Tue, 27 Nov 2007, Andrew Morton wrote:
>
> > The prefetch however might still need some work - we can indeed do
> > prefetch() against a not-possible CPU's memory here. And I do recall that
> > 4-5 years ago we did have a CPU (one of mine, iirc) which would oops when
> > prefetching from a bad address. I forget what the conclusion was on that
> > matter.
> >
> > If we do want to fix the prefetch-from-outer-space then we should be using
> > cpu_isset(cpu, *cpumask) here rather than cpu_possible().
>
> Generally the prefetch things have turned out to be not that useful. How
> about dropping the prefetch? I kept it because it was there.

I don't recall anyone ever demonstrating that prefetch is useful in-kernel.

I think I've heard of situations where benefits have been seen in userspace
- if a loop does a lot of calculation on each datum which it fetches then
there's a good opportunity to pipeline the fetch with the on-core
crunching. But kernel doesn't do that sort of thing..

-
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: 2007-11-28 00:45    [W:0.053 / U:0.376 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site