Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754157AbYKKRWT (ORCPT ); Tue, 11 Nov 2008 12:22:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751767AbYKKRWL (ORCPT ); Tue, 11 Nov 2008 12:22:11 -0500 Received: from viefep18-int.chello.at ([213.46.255.22]:57998 "EHLO viefep18-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751594AbYKKRWK (ORCPT ); Tue, 11 Nov 2008 12:22:10 -0500 X-SourceIP: 213.46.9.244 Subject: Re: [RFC PATCH v3 5/5] sched: activate active load balancing in new idle cpus From: Peter Zijlstra To: svaidy@linux.vnet.ibm.com 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 In-Reply-To: <20081111170441.GT4646@dirshya.in.ibm.com> References: <20081110181526.562.69941.stgit@drishya.in.ibm.com> <20081110183343.562.72751.stgit@drishya.in.ibm.com> <1226411235.7685.1775.camel@twins> <20081111170441.GT4646@dirshya.in.ibm.com> Content-Type: text/plain Date: Tue, 11 Nov 2008 18:21:50 +0100 Message-Id: <1226424110.7685.2038.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3060 Lines: 74 On Tue, 2008-11-11 at 22:34 +0530, Vaidyanathan Srinivasan wrote: > * 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. Ah, right, thanks! Could you clarify this by adding a comment to this effect right before the added code? -- 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/