Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754374AbYKKRIb (ORCPT ); Tue, 11 Nov 2008 12:08:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752709AbYKKRIM (ORCPT ); Tue, 11 Nov 2008 12:08:12 -0500 Received: from ausmtp06.au.ibm.com ([202.81.18.155]:57437 "EHLO ausmtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752601AbYKKRIK (ORCPT ); Tue, 11 Nov 2008 12:08:10 -0500 Date: Tue, 11 Nov 2008 22:34:41 +0530 From: Vaidyanathan Srinivasan To: Peter Zijlstra Cc: Linux Kernel , Suresh B Siddha , Venkatesh Pallipadi , Ingo Molnar , Dipankar Sarma , Balbir Singh , Vatsa , Gautham R Shenoy , Andi Kleen , David Collier-Brown , Tim Connors , Max Krasnyansky Subject: Re: [RFC PATCH v3 5/5] sched: activate active load balancing in new idle cpus Message-ID: <20081111170441.GT4646@dirshya.in.ibm.com> Reply-To: svaidy@linux.vnet.ibm.com Mail-Followup-To: Peter Zijlstra , Linux Kernel , Suresh B Siddha , Venkatesh Pallipadi , Ingo Molnar , Dipankar Sarma , Balbir Singh , Vatsa , Gautham R Shenoy , Andi Kleen , David Collier-Brown , Tim Connors , Max Krasnyansky References: <20081110181526.562.69941.stgit@drishya.in.ibm.com> <20081110183343.562.72751.stgit@drishya.in.ibm.com> <1226411235.7685.1775.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1226411235.7685.1775.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2771 Lines: 70 * Peter Zijlstra [2008-11-11 14:47:15]: > On Tue, 2008-11-11 at 00:03 +0530, Vaidyanathan Srinivasan wrote: > > Active load balancing is a process by which migration thread > > is woken up on the target CPU in order to pull current > > running task on another package into this newly idle > > package. > > > > This method is already in use with normal load_balance(), > > this patch introduces this method to new idle cpus when > > sched_mc is set to POWERSAVINGS_BALANCE_WAKEUP. > > > > This logic provides effective consolidation of short running > > daemon jobs in a almost idle system > > > > The side effect of this patch may be ping-ponging of tasks > > if the system is moderately utilised. May need to adjust the > > iterations before triggering. > > OK, I'm so not getting this patch.. > > if normal newly idle balancing fails that means the other runqueue has > only a single task on it (or some other really stubborn stuff), so then > you go move that one task that is already running, from one cpu to > another. > > _why_? > > The only answer I can come up with is that you prefer one cpu's > idle-ness over another - which makes sense, as you try to get whole > packages idle. Your answer is correct. We want to move that one task from a non-idle cpu to this cpu that is just going to be idle. This is the same method used to move task in load_balance(), I have extended it for load_balance_newidle() to make the consolidation faster at sched_mc=2. > But I'm not seeing where that package logic is hidden.. The package logic comes from find_busiest_group(). If there are no imbalance, then find_busiest_group() will return NULL. However when sched_mc={1,2} then find_busiest_group() will select a group from which a running task may be pulled to this cpu in order to make the other package idle. If there is no opportunity to make a package idle and if there are no imbalance, then find_busiest_group() will return NULL and no action will be taken in load_balance_newidle(). Under normal task pull operation due to imbalance, there will be more than one task in the source run queue and move_tasks() will succeed. ld_moved will be true and the active balance code will not be triggered. If we enter a scenario where we are moving the only running task from another cpu, then this should have been suggested by find_busiest_group's sched_mc balance logic and thus moving that task will potentially freeup the source package. Thanks for the careful review. --Vaidy -- 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/