From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ravikiran G Thirumalai <kiran@scalex86.org>
Cc: Andrew Morton <akpm@osdl.org>,
linux-kernel@vger.kernel.org,
"Shai Fultheim (Shai@scalex86.org)" <shai@scalex86.org>
Subject: Re: [patch] Cache align futex hash buckets
Date: Tue, 21 Feb 2006 14:30:00 +1100 [thread overview]
Message-ID: <43FA8938.70006@yahoo.com.au> (raw)
In-Reply-To: <20060220233242.GC3594@localhost.localdomain>
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;
> -
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next prev parent reply other threads:[~2006-02-21 6:31 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-20 23:32 [patch] Cache align futex hash buckets Ravikiran G Thirumalai
2006-02-20 23:33 ` Andrew Morton
2006-02-20 23:34 ` Andrew Morton
2006-02-21 0:09 ` Ravikiran G Thirumalai
2006-02-21 0:23 ` Andrew Morton
2006-02-21 1:04 ` Ravikiran G Thirumalai
2006-02-21 1:09 ` Andrew Morton
2006-02-21 1:39 ` Ravikiran G Thirumalai
2006-02-21 14:44 ` Andi Kleen
2006-02-21 3:30 ` Nick Piggin [this message]
2006-02-21 18:33 ` Christoph Lameter
2006-02-21 23:14 ` Christoph Lameter
2006-02-22 0:40 ` Nick Piggin
2006-02-22 2:08 ` Andrew Morton
2006-02-22 2:35 ` Ravikiran G Thirumalai
2006-02-22 2:37 ` Nick Piggin
2006-02-22 20:17 ` Ravikiran G Thirumalai
2006-02-22 20:50 ` Andrew Morton
[not found] ` <20060223015144.GC3663@localhost.localdomain>
2006-02-23 2:08 ` Ravikiran G Thirumalai
2006-02-21 20:20 ` Ravikiran G Thirumalai
2006-02-22 0:45 ` Nick Piggin
2006-02-22 2:09 ` Andrew Morton
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