Re: [PATCH] percpu_counter: Fix __percpu_counter_sum()

Andrew Morton
2008-12-08T23:08:39Z

On Mon, 8 Dec 2008 18:00:47 -0500
Theodore Tso <tytso@mit.edu> wrote:

> On Mon, Dec 08, 2008 at 11:20:35PM +0100, Peter Zijlstra wrote:
> >
> > atomic_t is pretty good on all archs, but you get to keep the cacheline
> > ping-pong.
> >
>
> Stupid question --- if you're worried about cacheline ping-pongs, why
> aren't each cpu's delta counter cacheline aligned?

They are allocated with alloc_percpu(), so each CPU's counter lives
in a per-cpu area. If you chase through seventeen layers of Rustyness
you end up at mm/allocpercpu.c:percpu_populate() which is where that
little s32 ends up getting allocated.