Re: [patch] Cache align futex hash buckets

[Andrew Morton]

Ravikiran G Thirumalai <kiran@xxxxxxxxxxxx> wrote:
>
> On Mon, Feb 20, 2006 at 03:34:19PM -0800, Andrew Morton wrote:
> > Andrew Morton <akpm@xxxxxxxx> 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.
-
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