From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758534AbdELURv (ORCPT ); Fri, 12 May 2017 16:17:51 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:44016 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758415AbdELURu (ORCPT ); Fri, 12 May 2017 16:17:50 -0400 Subject: Re: [PATCH 1/2] sched: Interrupt Aware Scheduler To: Peter Zijlstra References: <1494612267-29465-1-git-send-email-rohit.k.jain@oracle.com> <1494612267-29465-2-git-send-email-rohit.k.jain@oracle.com> <20170512194658.GG4626@worktop.programming.kicks-ass.net> Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, Morten Rasmussen , Dietmar Eggemann , Vincent Guittot From: Rohit Jain Message-ID: Date: Fri, 12 May 2017 13:19:50 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170512194658.GG4626@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/12/2017 12:46 PM, Peter Zijlstra wrote: > On Fri, May 12, 2017 at 11:04:26AM -0700, Rohit Jain wrote: >> The patch avoids CPUs which might be considered interrupt-heavy when >> trying to schedule threads (on the push side) in the system. Interrupt >> Awareness has only been added into the fair scheduling class. >> >> It does so by, using the following algorithm: >> -------------------------------------------------------------------------- >> 1) When the interrupt is getting processed, the start and the end times >> are noted for the interrupt on a per-cpu basis. > IRQ_TIME_ACCOUNTING you mean? Yes. Exactly >> 2) On a periodic basis the interrupt load is processed for each run >> queue and this is mapped in terms of percentage in a global array. The >> interrupt load for a given CPU is also decayed over time, so that the >> most recent interrupt load has the biggest contribution in the interrupt >> load calculations. This would mean the scheduler will try to avoid CPUs >> (if it can) when scheduling threads which have been recently busy with >> handling hardware interrupts. > You mean like like how its already added to rt_avg? Which is then used > to lower a CPU's capacity. Right. The only difference I see is that it is not being used on the enqueue side as of now. >> 3) Any CPU which lies above the 80th percentile in terms of percentage >> interrupt load is considered interrupt-heavy. >> >> 4) During idle CPU search from the scheduler perspective this >> information is used to skip CPUs if better are available. >> >> 5) If none of the CPUs are better in terms of idleness and interrupt >> load, then the interrupt-heavy CPU is considered to be the best >> available CPU. > I would much rather you work with the EAS people and extend the capacity > awareness of those code paths. Then, per the existing logic, things > should just work out. Did you mean we should use the capacity as a metric on the enqueue side and not introduce a new metric? > > It doesn't matter how the capacity is lowered, at some point you just > don't want to put tasks on. It really doesn't matter if that's because > IRQs, SoftIRQs, (higher priority) Real-Time tasks, thermal throttling or > anything else.