From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 650156B01C0 for ; Tue, 23 Mar 2010 14:27:43 -0400 (EDT) Date: Tue, 23 Mar 2010 19:27:35 +0100 From: Ingo Molnar Subject: Re: [Bugme-new] [Bug 15618] New: 2.6.18->2.6.32->2.6.33 huge regression in performance Message-ID: <20100323182735.GA10897@elte.hu> References: <20100323102208.512c16cc.akpm@linux-foundation.org> <20100323173409.GA24845@elte.hu> <20100323111351.756c8752.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100323111351.756c8752.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Linus Torvalds , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bugzilla-daemon@bugzilla.kernel.org, bugme-daemon@bugzilla.kernel.org, ant.starikov@gmail.com, Peter Zijlstra List-ID: * Andrew Morton wrote: > On Tue, 23 Mar 2010 18:34:09 +0100 > Ingo Molnar wrote: > > > > > It shows a very brutal amount of page fault invoked mmap_sem spinning > > overhead. > > > > Yes. Note that we fall off a cliff at nine threads on a 16-way. As soon as > a core gets two threads scheduled onto it? it's AMD Opterons so no SMT. My (wild) guess would be that 8 cpus can still do cacheline ping-pong reasonably efficiently, but it starts breaking down very seriously with 9 or more cores bouncing the same single cache-line. Breakdowns in scalability are usually very non-linear, for hardware and software reasons. '8 threads' sounds like a hw limit to me. From the scheduler POV there's no big difference between 8 or 9 CPUs used [this is non-HT] - with 8 or 7 cores still idle. Ingo -- 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