Re: [patch] Cache align futex hash buckets

[Ravikiran G Thirumalai <kiran@scalex86.org>]

On Mon, Feb 20, 2006 at 03:34:19PM -0800, Andrew Morton wrote:
> Andrew Morton <akpm@osdl.org> 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?

Thanks,
Kiran