From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751439AbeAWQ5k (ORCPT ); Tue, 23 Jan 2018 11:57:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43932 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751259AbeAWQ5j (ORCPT ); Tue, 23 Jan 2018 11:57:39 -0500 Message-ID: <1516726652.2554.58.camel@redhat.com> Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3 From: Paolo Abeni To: David Miller 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 Date: Tue, 23 Jan 2018 17:57:32 +0100 In-Reply-To: <20180123.112201.1263563609292212852.davem@davemloft.net> References: <1516376774-24076-1-git-send-email-frederic@kernel.org> <1516702432.2554.37.camel@redhat.com> <20180123.112201.1263563609292212852.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 Tue, 2018-01-23 at 11:22 -0500, David Miller wrote: > 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? As far as I can see, no: the workqueue thread has the same priority and nice level than the user space process. > Or is it that the workqueue execution is simply not yielding for some > reason? It's like that. I spent little time on it, so I haven't many data point. I'll try to investigate the scenario later this week. Cheers, Paolo