From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751807AbeAWQWF (ORCPT ); Tue, 23 Jan 2018 11:22:05 -0500 Received: from shards.monkeyblade.net ([184.105.139.130]:55316 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750994AbeAWQWE (ORCPT ); Tue, 23 Jan 2018 11:22:04 -0500 Date: Tue, 23 Jan 2018 11:22:01 -0500 (EST) Message-Id: <20180123.112201.1263563609292212852.davem@davemloft.net> To: pabeni@redhat.com Cc: frederic@kernel.org, linux-kernel@vger.kernel.org, alexander.levin@verizon.com, peterz@infradead.org, mchehab@s-opensource.com, torvalds@linux-foundation.org, 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 Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3 From: David Miller In-Reply-To: <1516702432.2554.37.camel@redhat.com> References: <1516376774-24076-1-git-send-email-frederic@kernel.org> <1516702432.2554.37.camel@redhat.com> X-Mailer: Mew version 6.7 on Emacs 25.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paolo Abeni Date: Tue, 23 Jan 2018 11:13:52 +0100 > Hi, > > On Fri, 2018-01-19 at 16:46 +0100, Frederic Weisbecker wrote: >> As per Linus suggestion, this take doesn't limit the number of occurences >> per jiffy anymore but instead defers a vector to workqueues as soon as >> it gets re-enqueued on IRQ tail. >> >> No tunable here, so testing should be easier. >> >> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git >> softirq/thread-v3 >> >> HEAD: 6835e92cbd70ef4a056987d2e1ed383b294429d4 > > I tested this series in the UDP flood scenario, binding the user space > process receiving the packets on the same CPU processing the related > IRQ, and the tput sinks nearly to 0, like before Eric's patch. > > The perf tool says that almost all the softirq processing is done > inside the workqueue, but the user space process is scheduled very > rarely, while before this series, in this scenario, ksoftirqd and the > user space process got a fair share of the CPU time. Do workqueue threads get a higher scheduling priority than user processes? If so, that's going to work against the entire point of deferring softirq work into a thread. Or is it that the workqueue execution is simply not yielding for some reason?