Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964996AbWHHQtb (ORCPT ); Tue, 8 Aug 2006 12:49:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964997AbWHHQtb (ORCPT ); Tue, 8 Aug 2006 12:49:31 -0400 Received: from pfx2.jmh.fr ([194.153.89.55]:3243 "EHLO pfx2.jmh.fr") by vger.kernel.org with ESMTP id S964996AbWHHQta (ORCPT ); Tue, 8 Aug 2006 12:49:30 -0400 From: Eric Dumazet To: Nick Piggin Subject: Re: [RFC] NUMA futex hashing Date: Tue, 8 Aug 2006 18:49:28 +0200 User-Agent: KMail/1.9.1 Cc: Ulrich Drepper , Andi Kleen , Ravikiran G Thirumalai , "Shai Fultheim (Shai@scalex86.org)" , pravin b shelar , linux-kernel@vger.kernel.org References: <20060808070708.GA3931@localhost.localdomain> <200608081808.34708.dada1@cosmosbay.com> <44D8BD29.4010102@yahoo.com.au> In-Reply-To: <44D8BD29.4010102@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200608081849.28458.dada1@cosmosbay.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1196 Lines: 28 On Tuesday 08 August 2006 18:34, Nick Piggin wrote: > Eric Dumazet wrote: > > We certainly can. But if you insist of using mmap sem at all, then we > > have a problem. > > > > rbtree would not reduce cacheline bouncing, so : > > > > We could use a hashtable (allocated on demand) of size N, N depending on > > NR_CPUS for example. each chain protected by a private spinlock. If N is > > well chosen, we might reduce lock cacheline bouncing. (different threads > > fighting on different private futexes would have a good chance to get > > different cachelines in this hashtable) > > See other mail. We already have a hash table ;) Yes but still you want at FUTEX_WAIT time to tell the kernel the futex is private to this process. Giving the same info at FUTEX_WAKE time could avoid the kernel to make the second pass (using only a private futex lookup), avoiding again the mmap_sem touch in case no threads are waiting anymore on this futex. Eric - 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/