Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753736AbbEIHEJ (ORCPT ); Sat, 9 May 2015 03:04:09 -0400 Received: from mail-wi0-f177.google.com ([209.85.212.177]:35620 "EHLO mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753553AbbEIHEG (ORCPT ); Sat, 9 May 2015 03:04:06 -0400 Message-ID: <1431155043.3209.125.camel@gmail.com> Subject: Re: [PATCH 3/6] dataplane nohz: run softirqs synchronously on user entry From: Mike Galbraith To: Chris Metcalf Cc: Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Peter Zijlstra , Andrew Morton , Rik van Riel , Tejun Heo , Frederic Weisbecker , "Paul E. McKenney" , Christoph Lameter , "Srivatsa S. Bhat" , linux-kernel@vger.kernel.org Date: Sat, 09 May 2015 09:04:03 +0200 In-Reply-To: <1431107927-13998-4-git-send-email-cmetcalf@ezchip.com> References: <1431107927-13998-1-git-send-email-cmetcalf@ezchip.com> <1431107927-13998-4-git-send-email-cmetcalf@ezchip.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 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 Content-Length: 1038 Lines: 21 On Fri, 2015-05-08 at 13:58 -0400, Chris Metcalf wrote: > For tasks which have elected dataplane functionality, we run > any pending softirqs for the core before returning to userspace, > rather than ever scheduling ksoftirqd to run. The problem we > fix is that by allowing another task to run on the core, we > guarantee more interrupts in the future to the dataplane task, > which is exactly what dataplane mode is required to prevent. If ksoftirqd were rt class, softirqs would be gone when the soloist gets the CPU back and heads to userspace. Being a soloist, it has no use for a priority, so why can't it just let ksoftirqd run if it raises the occasional softirq? Meeting a contended lock while processing it will wreck the soloist regardless of who does that processing. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/