From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Travis Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected Date: Tue, 26 Aug 2008 13:01:02 -0700 Message-ID: <48B460FE.2020100@sgi.com> References: <48B29F7B.6080405@hp.com> <48B2A421.7080705@hp.com> <48B313E0.1000501@hp.com> <48B452F3.9040304@sgi.com> <20080826192848.GA20653@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080826192848.GA20653-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Dave Jones , Linus Torvalds , Mike Travis , "Alan D. Brunelle" , Ingo Molnar Dave Jones wrote: ... > > But yes, for this to be even remotely feasible, there has to be a negligable > performance cost associated with it, which right now, we clearly don't have. > Given that the number of people running 4096 CPU boxes even in a few years time > will still be tiny, punishing the common case is obviously absurd. > > Dave > I did do some fairly extensive benchmarking between configs of NR_CPUS = 128 and 4096 and most performance hits were in the neighborhood of < 5% on systems with 8 cpus and 4GB of memory (our most common test system). [But changing cpumask_t's to be pointers instead of values will likely increase this.] I've tried to be very sensitive to this issue with all my previous changes, so convincing the distros to set NR_CPUS=4096 would be as painless for them as possible. ;-) Btw, huge count cpu systems I don't think are that far away. I believe the nextgen Larabbee chips will be geared towards HPC applications [instead of just GFX apps], and putting 4 of these chips on a motherboard would add up to 512 cpu threads (1024 if they support hyperthreading.) Thanks, Mike