Re: [patch] Cache align futex hash buckets

[Andrew Morton <akpm@osdl.org>]

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?
-
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