From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934279AbeAXQLV (ORCPT ); Wed, 24 Jan 2018 11:11:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44112 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934021AbeAXQLU (ORCPT ); Wed, 24 Jan 2018 11:11:20 -0500 Message-ID: <1516810271.2476.43.camel@redhat.com> Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3 From: Paolo Abeni To: David Miller Cc: torvalds@linux-foundation.org, frederic@kernel.org, linux-kernel@vger.kernel.org, alexander.levin@verizon.com, peterz@infradead.org, mchehab@s-opensource.com, hannes@stressinduktion.org, paulmck@linux.vnet.ibm.com, wanpeng.li@hotmail.com, dima@arista.com, tglx@linutronix.de, akpm@linux-foundation.org, rrendec@arista.com, mingo@kernel.org, sgruszka@redhat.com, riel@redhat.com, edumazet@google.com, nks.gnu@gmail.com Date: Wed, 24 Jan 2018 17:11:11 +0100 In-Reply-To: <20180124.100558.97132829347179555.davem@davemloft.net> References: <1516726652.2554.58.camel@redhat.com> <1516805645.2476.23.camel@redhat.com> <20180124.100558.97132829347179555.davem@davemloft.net> Content-Type: text/plain; charset="UTF-8" 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 On Wed, 2018-01-24 at 10:05 -0500, David Miller wrote: > From: Paolo Abeni > Date: Wed, 24 Jan 2018 15:54:05 +0100 > > > Niklas suggested a possible relation with CONFIG_IRQ_TIME_ACCOUNTING=y > > and indeed he was right. > > > > The patched kernel under test had CONFIG_IRQ_TIME_ACCOUNTING set, and > > very little CPU time was accounted to the kworker: > > > > [2125 is the relevant kworker's pid] > > grep sum_exec_runtime /proc/2125/sched; sleep 10; grep sum_exec_runtime /proc/2125/sched > > se.sum_exec_runtime : 13408.239286 > > se.sum_exec_runtime : 13456.907197 > > > > despite such process was processing a lot of packets and basically > > burning a CPU. > > So IRQ_TIME_ACCOUNTING makes the scheduler think that the worker > threads are using nearly no task time at all. Yes, this is the behavior I observe in the test. But a quick look at the scheduler code - I'm not very familiar with it - let me think this is not the intended/expected behaviour for the ksoftirqd (and after this series, for the kworker serving the softirq). > The existing ksoftirqd code should hit the same problem, right? I just tried the vanilla kernel with CONFIG_IRQ_TIME_ACCOUNTING=y, and in the same test scenario, I observe the 'good' behavior: the user space process and ksoftirqd share almost fairly the relevant CPU, and the CPU time spend in softirq processing is accounted to ksoftirqd. Cheers, Paolo