Messages in this thread | | | Date | Tue, 21 Feb 2006 14:30:00 +1100 | From | Nick Piggin <> | Subject | Re: [patch] Cache align futex hash buckets |
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Ravikiran G Thirumalai 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. >
It does not make sense to add swaths of unused memory into a hashtable for this purpose, does it?
For a minimal, naive solution you just increase the size of the hash table. This will (given a decent hash function) provide the same reduction in cacheline contention, while also reducing collisions.
A smarter solution might have a single lock per cacheline, and multiple hash slots. This could make the indexing code a bit more awkward though.
> 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; > > /* Futex-fs vfsmount entry: */ > static struct vfsmount *futex_mnt; > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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