lkml.org 
[lkml]   [2006]   [Aug]   [8]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC] NUMA futex hashing
FromAndi Kleen <>
Date08 Aug 2006 11:57:59 +0200
Ravikiran G Thirumalai <kiran@scalex86.org> writes:

> Current futex hash scheme is not the best for NUMA.   The futex hash table is 
> an array of struct futex_hash_bucket, which is just a spinlock and a 
> list_head -- this means multiple spinlocks on the same cacheline and on NUMA 
> machines, on the same internode cacheline.  If futexes of two unrelated 
> threads running on two different nodes happen to hash onto adjacent hash 
> buckets, or buckets on the same internode cacheline, then we have the 
> internode cacheline bouncing between nodes.

When I did some testing with a (arguably far too lock intensive) benchmark
on a bigger box I got most bouncing cycles not in the futex locks itself,
but in the down_read on the mm semaphore.

I guess that is not addressed?

-Andi
-
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/

\
 
 \ /
  Last update: 2006-08-08 12:03    [from the cache]
©2003-2008