From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5379C28CC0 for ; Wed, 29 May 2019 14:52:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8AEFD23AB8 for ; Wed, 29 May 2019 14:52:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726753AbfE2Owr (ORCPT ); Wed, 29 May 2019 10:52:47 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:54874 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726012AbfE2Owr (ORCPT ); Wed, 29 May 2019 10:52:47 -0400 Received: from p200300d06f28ff00b92b307fdbdaf2b9.dip0.t-ipconnect.de ([2003:d0:6f28:ff00:b92b:307f:dbda:f2b9] helo=somnus.fritz.box) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hVzwZ-0005zw-9x; Wed, 29 May 2019 16:52:43 +0200 Date: Wed, 29 May 2019 16:52:37 +0200 (CEST) From: Anna-Maria Gleixner To: Marcelo Tosatti cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Thomas Gleixner , Daniel Bristot de Oliveira , Luiz Capitulino , Haris Okanovic Subject: Re: [patch 0/3] do not raise timer softirq unconditionally (spinlockless version) In-Reply-To: <20190415201213.600254019@amt.cnet> Message-ID: References: <20190415201213.600254019@amt.cnet> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I had a look at the queue and have several questions about your implementation. First of all, I had some troubles to understand your commit messages. So I first had to read the code and then tried to understand the commit messages. It is easier, if it works the other way round. On Mon, 15 Apr 2019, Marcelo Tosatti wrote: > For isolated CPUs, we'd like to skip awakening ktimersoftd > (the switch to and then back from ktimersoftd takes 10us in > virtualized environments, in addition to other OS overhead, > which exceeds telco requirements for packet forwarding for > 5G) from the sched tick. You would like to prevent raising the timer softirq in general from the sched tick for isolated CPUs? Or you would like to prevent raising the timer softirq if no pending timer is available? Nevertheless, this change is not PREEMPT_RT specific. It is a NOHZ dependand change. So it would be nice, if the queue is against mainline. But please correct me, if I'm wrong. [...] > This patchset reduces cyclictest latency from 25us to 14us > on my testbox. > A lot of information is missing: How does your environment looks like for this test, what is your workload,...? Did you also run other tests? Thanks, Anna-Maria