Ravikiran G Thirumalai <[email protected]> wrote:
>
> On Mon, Feb 20, 2006 at 04:23:17PM -0800, Andrew Morton wrote:
> > Ravikiran G Thirumalai <[email protected]> wrote:
> > >
> > > On Mon, Feb 20, 2006 at 03:34:19PM -0800, Andrew Morton wrote:
> > > > Andrew Morton <[email protected]> wrote:
> > > > >
> > > > > > @@ -100,9 +100,10 @@ struct futex_q {
> > > > > > struct futex_hash_bucket {
> > > > > > spinlock_t lock;
> > > > > > struct list_head chain;
> > > > > > -};
> > > > > > +} ____cacheline_internodealigned_in_smp;
> > > > > >
> > > > > > -static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
> > > > > > +static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS]
> > > > > > + __cacheline_aligned_in_smp;
> > > > > >
> > > > >
> > > > > How much memory does that thing end up consuming?
> > > >
> > > > I think a megabyte?
> > >
> > > On most machines it would be 256 * 128 = 32k. or 16k on arches with 64B
> > > cachelines. This looked like a simpler solution for spinlocks falling on
> > > the same cacheline. So is 16/32k unreasonable?
> > >
> >
> > CONFIG_X86_VSMP enables 4096-byte padding for
> > ____cacheline_internodealigned_in_smp. It's a megabyte.
>
> Yes, only on vSMPowered systems. Well, we have a large
> internode cacheline, but these machines have lots of memory too. I
> thought a simpler padding solution might be acceptable as futex_queues
> would be large only on our boxes.
Well it's your architecture... As long as you're finding this to be a
sufficiently large problem in testing to justify consuming a meg of memory
then fine, let's do it.
But your initial changelog was rather benchmark-free? It's always nice to
see numbers accompanying a purported optimisation patch.
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