From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756594AbcDLUIJ (ORCPT ); Tue, 12 Apr 2016 16:08:09 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:48678 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751181AbcDLUIH (ORCPT ); Tue, 12 Apr 2016 16:08:07 -0400 Date: Tue, 12 Apr 2016 16:07:28 -0400 From: Chris Mason To: Mike Galbraith CC: Peter Zijlstra , Ingo Molnar , Matt Fleming , Subject: Re: sched: tweak select_idle_sibling to look for idle threads Message-ID: <20160412200728.GA41928@clm-mbp.thefacebook.com> Mail-Followup-To: Chris Mason , Mike Galbraith , Peter Zijlstra , Ingo Molnar , Matt Fleming , linux-kernel@vger.kernel.org References: <20160405180822.tjtyyc3qh4leflfj@floor.thefacebook.com> <20160409190554.honue3gtian2p6vr@floor.thefacebook.com> <1460282661.4251.44.camel@suse.de> <20160410195543.fp2tpixaafsts5x3@floor.thefacebook.com> <1460350461.3870.36.camel@suse.de> <20160412003044.smr24xzuom3locvo@floor.thefacebook.com> <1460436248.3839.80.camel@suse.de> <20160412132758.7apgqqwl2c2wksy6@floor.thefacebook.com> <1460484977.5617.32.camel@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1460484977.5617.32.camel@suse.de> User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [192.168.52.123] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-04-12_10:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 12, 2016 at 08:16:17PM +0200, Mike Galbraith wrote: > On Tue, 2016-04-12 at 09:27 -0400, Chris Mason wrote: > > I > > can always add the tunable to flip things on/off but I'd prefer that we > > find a good set of defaults, mostly so the FB production runtime is the > > common config instead of the special snowflake. > > Yeah, generic has a much better chance to actually get merged, just > need a very solid chain on the lurking beast from hell. Hm... > > The last time we went through this, the problem child was the waker of > many in your load. With tiny twiddle to wake_wide(), all was allegedly > well, or at least that's the impression I was left with. That leads me > to a pseudo-random thought: iff that waker of many is still at the > root, you could try using wake_wide() as the full search trigger, which > should shrink the attack surface available to the horror-from-hell > quite a lot. Just a thought. I think that if we're worried about the cost of the idle scan for this workload, find_idlest_group() is either going to hurt much more, or not search enough CPUs to find the idle one. But I'm happy to try patches or other ideas, I have a fixed version of the bitmap one going through production benchmarks now. -chris