From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753360AbeENRgM (ORCPT ); Mon, 14 May 2018 13:36:12 -0400 Received: from esa2.hgst.iphmx.com ([68.232.143.124]:37589 "EHLO esa2.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752347AbeENRgG (ORCPT ); Mon, 14 May 2018 13:36:06 -0400 X-IronPort-AV: E=Sophos;i="5.49,400,1520870400"; d="scan'208";a="174675123" Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Bart.VanAssche@wdc.com; Subject: Re: [PATCH 0/7] psi: pressure stall information for CPU, memory, and IO To: Christopher Lameter , Johannes Weiner Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, cgroups@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Andrew Morton , Tejun Heo , Balbir Singh , Mike Galbraith , Oliver Yang , Shakeel Butt , xxx xxx , Taras Kondratiuk , Daniel Walker , Vinayak Menon , Ruslan Ruslichenko , kernel-team@fb.com References: <20180507210135.1823-1-hannes@cmpxchg.org> <010001635f4e8be9-94e7be7a-e75c-438c-bffb-5b56301c4c55-000000@email.amazonses.com> From: Bart Van Assche Message-ID: Date: Mon, 14 May 2018 10:35:37 -0700 User-Agent: Mozilla/5.0 (X11; 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If CPU utilization is at 100% and CPU >> pressure is 0, it means the system is perfectly utilized, with one >> runnable thread per CPU and nobody waiting. At two or more runnable >> tasks per CPU, the system is 100% overcommitted and the pressure >> average will indicate as much. From a utilization perspective this is >> a great state of course: no CPU cycles are being wasted, even when 50% >> of the threads were to go idle (and most workloads do vary). From the >> perspective of the individual job it's not great, however, and they >> might do better with more resources. Depending on what your priority >> is, an elevated "some" number may or may not require action. > > This looks awfully similar to loadavg. Problem is that loadavg gets > screwed up by tasks blocked waiting for I/O. Isnt there some way to fix > loadavg instead? The following article explains why it probably made sense in 1993 to include TASK_UNINTERRUPTIBLE in loadavg and also why this no longer makes sense today: http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html Bart.