Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932905AbcDLSQV (ORCPT ); Tue, 12 Apr 2016 14:16:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:48184 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753645AbcDLSQT (ORCPT ); Tue, 12 Apr 2016 14:16:19 -0400 Message-ID: <1460484977.5617.32.camel@suse.de> Subject: Re: sched: tweak select_idle_sibling to look for idle threads From: Mike Galbraith To: Chris Mason Cc: Peter Zijlstra , Ingo Molnar , Matt Fleming , linux-kernel@vger.kernel.org Date: Tue, 12 Apr 2016 20:16:17 +0200 In-Reply-To: <20160412132758.7apgqqwl2c2wksy6@floor.thefacebook.com> 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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 848 Lines: 18 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. -Mike