[lkml]   [2009]   [Jan]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] percpu: add optimized generic percpu accessors
On Wed, 21 Jan 2009 03:21:23 -0800 (Eric W. Biederman) wrote:

> Tejun Heo <> writes:
> > Ingo Molnar wrote:
> >> The larger point still remains: the kernel dominantly uses static percpu
> >> variables by a margin of 10 to 1, so we cannot just brush away the static
> >> percpu variables and must concentrate on optimizing that side with
> >> priority. It's nice if the dynamic percpu-alloc side improves as well, of
> >> course.
> >
> > Well, the infrequent usage of dynamic percpu allocation is in some
> > part due to the poor implementation, so it's sort of chicken and egg
> > problem. I got into this percpu thing because I wanted a percpu
> > reference count which can be dynamically allocated and it sucked.
> Counters are our other special case, and counters are interesting
> because they are individually very small. I just looked and the vast
> majority of the alloc_percpu users are counters.
> I just did a rough count in include/linux/snmp.h and I came
> up with 171*2 counters. At 8 bytes per counter that is roughly
> 2.7K. Or about two thirds of a 4K page.

This is crap. only a small fraction of these SNMP counters are
close enough to the hot path to deserve per-cpu treatment.

 \ /
  Last update: 2009-01-21 13:49    [W:0.524 / U:0.156 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site