From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 3 Apr 2007 16:44:55 -0700 From: Andrew Morton Subject: Re: missing madvise functionality Message-Id: <20070403164455.83ae7b36.akpm@linux-foundation.org> In-Reply-To: <20070403144948.fe8eede6.akpm@linux-foundation.org> References: <46128051.9000609@redhat.com> <46128CC2.9090809@redhat.com> <20070403172841.GB23689@one.firstfloor.org> <20070403125903.3e8577f4.akpm@linux-foundation.org> <4612B645.7030902@redhat.com> <20070403202937.GE355@devserv.devel.redhat.com> <20070403144948.fe8eede6.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Jakub Jelinek , Ulrich Drepper , Andi Kleen , Rik van Riel , Linux Kernel , linux-mm@kvack.org, Hugh Dickins List-ID: On Tue, 3 Apr 2007 14:49:48 -0700 Andrew Morton wrote: > > int > > main (void) > > { > > pthread_t th[32]; > > int i; > > for (i = 0; i < 32; i++) > > if (pthread_create (&th[i], NULL, tf, NULL)) > > exit (4); > > for (i = 0; i < 32; i++) > > pthread_join (th[i], NULL); > > return 0; > > } > > > > whee. 135,000 context switches/sec on a slow 2-way. mmap_sem, most > likely. That is ungood. > > Did anyone monitor the context switch rate with the mysql test? > > Interestingly, your test app (with s/100000/1000) runs to completion in 13 > seocnd on the slow 2-way. On a fast 8-way, it took 52 seconds and > sustained 40,000 context switches/sec. That's a bit unexpected. > > Both machines show ~8% idle time, too :( Rohit solved this puzzle. The 2-way is a single package, hyperthreaded. The 8-way is two-package, four cores in each. So on the 8-way, that lock is getting transferred between the two packages like crazy. Running the benchmark on just cpus 0 and 1 (taskset -c 0,1) took the runtime down to eight seconds (from 52!) and the context switch rate went up to 200,000/sec (from 45,000). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org