Re: [patch] Cache align futex hash buckets

[Andrew Morton <akpm@osdl.org>]

Andrew Morton <akpm@osdl.org> wrote:
>
> Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> >
> > Following change places each element of the futex_queues hashtable on a 
> > different cacheline.  Spinlocks of adjacent hash buckets lie on the same 
> > cacheline otherwise.
> > 
> > Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
> > Signed-off-by: Shai Fultheim <shai@scalex86.org>
> > 
> > Index: linux-2.6.16-rc2/kernel/futex.c
> > ===================================================================
> > --- linux-2.6.16-rc2.orig/kernel/futex.c	2006-02-07 23:14:04.000000000 -0800
> > +++ linux-2.6.16-rc2/kernel/futex.c	2006-02-09 14:04:22.000000000 -0800
> > @@ -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?
-
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