Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754380AbYFBUD1 (ORCPT ); Mon, 2 Jun 2008 16:03:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752189AbYFBUDR (ORCPT ); Mon, 2 Jun 2008 16:03:17 -0400 Received: from zcars04e.nortel.com ([47.129.242.56]:41507 "EHLO zcars04e.nortel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650AbYFBUDP (ORCPT ); Mon, 2 Jun 2008 16:03:15 -0400 Message-ID: <484451F7.5090001@nortel.com> Date: Mon, 02 Jun 2008 14:03:03 -0600 From: "Chris Friesen" User-Agent: Mozilla Thunderbird 1.0.2-6 (X11/20050513) X-Accept-Language: en-us, en MIME-Version: 1.0 To: vatsa@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, mingo@elte.hu, a.p.zijlstra@chello.nl, pj@sgi.com, Balbir Singh , aneesh.kumar@linux.vnet.ibm.com, dhaval@linux.vnet.ibm.com Subject: Re: fair group scheduler not so fair? References: <4834B75A.40900@nortel.com> <20080527171528.GD30285@linux.vnet.ibm.com> <483C4F5A.2010104@nortel.com> <20080528163318.GG30285@linux.vnet.ibm.com> <483DA5E7.5050600@nortel.com> <20080529164607.GC12836@linux.vnet.ibm.com> <483F207D.4010908@nortel.com> <20080530113653.GI12836@linux.vnet.ibm.com> In-Reply-To: <20080530113653.GI12836@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 02 Jun 2008 20:03:10.0738 (UTC) FILETIME=[AEB2EF20:01C8C4EB] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2043 Lines: 50 Srivatsa Vaddagiri wrote: > That seems to be pretty difficult to achieve with the per-cpu runqueue > and smpnice based load balancing approach we have now. Okay, thanks. >>Initially I tried a simple setup with three hogs all in the default "sys" >>group. Over multiple retries using 10-sec intervals, sometimes it gave >>roughly 67% for each task, other times it settled into a 100/50/50 split >>that remained stable over time. > Was this with imbalance_pct set to 105? Does it make any difference if > you change imbalance_pct to say 102? It was set to 105 initially. I later reproduced the problem with 102. For example, the following was with 102, with three tasks created in the sys class. Based on the runtime, pid 2499 has been getting a cpu all to itself for over a minute. 2499 cfriesen 20 0 3800 392 336 R 99.8 0.0 1:05.85 cat 2496 cfriesen 20 0 3800 392 336 R 50.0 0.0 0:32.95 cat 2498 cfriesen 20 0 3800 392 336 R 50.0 0.0 0:32.97 cat The next run was much better, with sub-second fairness after a minute. 2505 cfriesen 20 0 3800 392 336 R 68.2 0.0 1:00.32 cat 2506 cfriesen 20 0 3800 392 336 R 66.9 0.0 0:59.85 cat 2503 cfriesen 20 0 3800 392 336 R 64.2 0.0 1:00.21 cat The lack of predictability is disturbing, as it implies some sensitivity to the specific test conditions. >>With three groups, one task in each, I tried both 10 and 60 second >>intervals. The longer interval looked better but was still up to 0.8% off: > > > I honestly don't know if we can do better than 0.8%! In any case, I'd > expect that it would require more drastic changes. No problem. It's still far superior than the SMP performance of CKRM, which is what we're currently using (although heavily modified). Chris -- 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/