![]() | |||||||||||||
Messages in this thread |
On Tue, Aug 08, 2006 at 12:10:39PM +0200, Eric Dumazet wrote: > On Tuesday 08 August 2006 11:57, Andi Kleen wrote: > > 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. > > This is true, even with a normal application (not a biased benchmark) and > using oprofile. mmap_sem is the killer. Not if two threads of two different process (so no same mmap_sem) hash onto futexes on the same cacheline. But agreed, mmap_sem needs to be fixed too. If everyone agrees on a per-process hash table for private futexes, then we will work on that approach. Thanks, Kiran - 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: 2006-08-09 02:15 [from the cache] ©2003-2008 | |||||||||||||