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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9408DC433EF for ; Thu, 30 Sep 2021 00:13:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 777C561528 for ; Thu, 30 Sep 2021 00:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345040AbhI3APO (ORCPT ); Wed, 29 Sep 2021 20:15:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231238AbhI3APL (ORCPT ); Wed, 29 Sep 2021 20:15:11 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6784C06161C for ; Wed, 29 Sep 2021 17:13:29 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id oa12-20020a17090b1bcc00b0019f2d30c08fso3399395pjb.0 for ; Wed, 29 Sep 2021 17:13:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:references:date:in-reply-to:message-id :user-agent:mime-version:content-transfer-encoding; bh=95JsvCzQiPnDRFbySU6C/Kkfi9kUM94rpQI/r+qt14k=; b=n0uX4a+d1zqvxku2qxe047HVIkzuvrY49x0HqAt+BFXZEmzvgrWLA+n3nWc7KpcVRr mVhBenUF++JtA4deODUi/DfWA/lqIZe+I3iwNtyGh+PG2VVz9KmU3YhsQsg3Uqct6Xe/ WsSjEbIZyImwlAkSTNoFarEYvWdJy0PdgXNFrCWwhtTAu1RUWF6sS8YKfwLZQdd6/Tft f9IhdD+7GjYtd7suO4qRFPd+oxqJ3i14DtWVS3LY7z8cVXeZgzWMs2sAP9vgPJnxFNUo Cp2u+CaQNMuKW04md6nlmrTrPWN8lLetgybZq1sNhSN5jI9AnZppIH3/PLrt3LHB+E4G 4RXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:references:date:in-reply-to :message-id:user-agent:mime-version:content-transfer-encoding; bh=95JsvCzQiPnDRFbySU6C/Kkfi9kUM94rpQI/r+qt14k=; b=wDuWB1WmgBiQf3FJvZR4E/1F/Tg+Z29XYJdIHmdBFAxGUzwf8lr+q+M72l0HJlh54v 0NxA2E52cGpUBYamZfNukE/+Y7kDSyaSZG0aWVYQnxv1lz5mQLOJ6UvagH+3n8svh/kA sxjzvTHvO2Gy6gFEuvT6JiefDnKwWfUoF9I4/Z8zmI730XBXQYDQ4odW0Rzt/LTSD/EX cytuOiV5sXOKKUd78IovmKlNB7AiAkQRSVyguEmqEio/g8XaDIW5LRp3FrYU1A2CbyCp XgCXT9d89lz6NZ9cFjHSCDkp+8yUGAxUdq33iTYiYq5y76ABr6S+JLw9sLx37qHR3v9b vzkw== X-Gm-Message-State: AOAM533YP1+o63LNca3peX7jvZuzkxL5Ia/tLGVTOhKYlFtATmNsSpdc 8BwUOVY/FloL7ouTG/GHDQhgDyIwxFA= X-Google-Smtp-Source: ABdhPJzRqkXQz+Vy3PCfd4/29W31OenJEj+1d4Cjvgwy5sAYDRaarVkZTzKqzQRwPrTbBgGsLV4B5w== X-Received: by 2002:a17:902:d507:b0:13e:1145:b1cd with SMTP id b7-20020a170902d50700b0013e1145b1cdmr2505957plg.19.1632960809246; Wed, 29 Sep 2021 17:13:29 -0700 (PDT) Received: from localhost (122x211x248x161.ap122.ftth.ucom.ne.jp. [122.211.248.161]) by smtp.gmail.com with ESMTPSA id c199sm792149pfb.152.2021.09.29.17.13.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Sep 2021 17:13:28 -0700 (PDT) From: Punit Agrawal To: Pierre FICHEUX Cc: linux-rt-users@vger.kernel.org Subject: Re: Strange problem with PREEMPT_RT References: Date: Thu, 30 Sep 2021 09:13:25 +0900 In-Reply-To: (Pierre FICHEUX's message of "Wed, 29 Sep 2021 18:40:35 +0200") Message-ID: <87y27e53a2.fsf@stealth> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org Pierre FICHEUX writes: > Hi, > > I have a strange problem on a PREEMPT_RT system. > > I have a process with 2 threads, > > - 1 TR thread (10 ms period) which places 350 KB blocks in a fifo (1 > block every 10 ms). > - 1 non-TR thread (SCHED_OTHER) which reads the block in the fifo and > writes it to the disk > > If I run this on a powerful machine (HP Z4-i9, 14 cores, NVME disk, > CentOS 7 with 3.10 PREEMPT_RT kernel, yes that's ooold), the max > jitter WITH hackbench remains around 20 to 30 =C2=B5s while the max jitter > WITHOUT hackbench goes up to 350 =C2=B5s! > > -> hackbench -p -g 20 -l 10000000 > > Running the program with taskset 01 doesn't change anything > If I don't write the data to disk it doesn't change anything either. > > The important jitters appear rather at the beginning (but sometimes also = later). > > Any ideas ? Is power management (cpuidle, cpufreq) enabled on the system? One possible explanation - The load from the 10ms task, isn't high enough to keep the system at high-frequencies or prevent it from going into deeper sleep states. Both of these can impact latencies. With hackbench, the system is sufficiently busy to avoid the going into idle. > > > thanks by advance > > -- > Pierre