From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758628AbYGaTxU (ORCPT ); Thu, 31 Jul 2008 15:53:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750751AbYGaTxB (ORCPT ); Thu, 31 Jul 2008 15:53:01 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:55431 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937AbYGaTxA (ORCPT ); Thu, 31 Jul 2008 15:53:00 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Robin Holt Cc: "Eric W. Biederman" , linux-kernel@vger.kernel.org, Pavel Emelyanov , Oleg Nesterov , Sukadev Bhattiprolu , Paul Menage , Linus Torvalds , Andrew Morton References: <20080731170022.GE9663@sgi.com> <20080731193204.GG9663@sgi.com> Date: Thu, 31 Jul 2008 12:49:35 -0700 In-Reply-To: <20080731193204.GG9663@sgi.com> (Robin Holt's message of "Thu, 31 Jul 2008 14:32:04 -0500") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SA-Exim-Connect-IP: 24.130.11.59 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa03 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Robin Holt X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -1.1 BAYES_05 BODY: Bayesian spam probability is 1 to 5% * [score: 0.0162] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 XM_SPF_Neutral SPF-Neutral Subject: Re: [Patch] Scale pidhash_shift/pidhash_size up based on num_possible_cpus(). X-SA-Exim-Version: 4.2 (built Thu, 03 Mar 2005 10:44:12 +0100) X-SA-Exim-Scanned: Yes (on mgr1.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Robin Holt writes: > On Thu, Jul 31, 2008 at 11:35:19AM -0700, Eric W. Biederman wrote: >> Robin Holt writes: >> >> > For large cpu configurations, we find the number of pids in a pidhash >> > bucket cause things like 'ps' to perform slowly. Raising pidhash_shift >> > from 12 to 16 cut the time for 'ps' in half on a 2048 cpu machine. >> > >> > This patch makes the upper limit scale based upon num_possible_cpus(). >> > For machines 128 cpus or less, the current upper limit of 12 is >> > maintained. >> >> It looks like there is a magic limit we are dancing around. >> >> Can we please make the maximum for the hash table size be based >> on the maximum number of pids. That is fls(PID_MAX_LIMIT) - 6? > > I am happy to base it upon whatever you think is correct. So long as it > goes up for machines with lots of cpus, that will satisfy me. It is > probably as much a problem on smaller machines, but if you have _THAT_ > many pids in use, you are probably oversubscribing many other resources > and don't really care. That limit will essentially become a constant > (compiler may even do that for us but I have not checked any arch other > that ia64). Should I just replace the 12 with a 16 or 17 or some new > magic number? I like setting the limit as a maximum hash chain length. Which is what fls(PID_MAX_LIMIT) - X is. X is the maximum hash chain length you can tolerate. Eric