From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751229AbWFBWH2 (ORCPT ); Fri, 2 Jun 2006 18:07:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751255AbWFBWH2 (ORCPT ); Fri, 2 Jun 2006 18:07:28 -0400 Received: from mail30.syd.optusnet.com.au ([211.29.133.193]:1452 "EHLO mail30.syd.optusnet.com.au") by vger.kernel.org with ESMTP id S1751229AbWFBWH1 (ORCPT ); Fri, 2 Jun 2006 18:07:27 -0400 From: Con Kolivas To: "Chen, Kenneth W" Subject: Re: [PATCH RFC] smt nice introduces significant lock contention Date: Sat, 3 Jun 2006 08:04:07 +1000 User-Agent: KMail/1.9.1 Cc: linux-kernel@vger.kernel.org, "Nick Piggin" , "'Chris Mason'" , "Ingo Molnar" References: <000201c6868f$14ddbfc0$df34030a@amr.corp.intel.com> In-Reply-To: <000201c6868f$14ddbfc0$df34030a@amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200606030804.08382.kernel@kolivas.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 03 June 2006 07:54, Chen, Kenneth W wrote: > Con Kolivas wrote on Friday, June 02, 2006 6:17 AM > > Thinking some more on this it is also clear that the concept of > > per_cpu_gain for smt is basically wrong once we get beyond straight > > forward 2 thread hyperthreading. If we have more than 2 thread units per > > physical core, the per cpu gain per logical core will decrease the more > > threads are running on it. While it's always been obvious the gain per > > logical core is entirely dependant on the type of workload and wont be a > > simple 25% increase in cpu power, it is clear that even if we assume an > > "overall" increase in cpu for each logical core added, there will be some > > non linear function relating power increase to thread units used. :-| > > In the context of having more than 2 sibling CPUs in a domain, doesn't the > current code also suffer from thunder hurd problem as well? When high > priority task goes to sleep, it will wake up *all* sibling sleepers and > then they will all fight for CPU resource, but potentially only one will > win? Yes. The smt nice code was never designed with that many threads in mind. This is why I'm bringing it up for discussion. -- -ck