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=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 4256FC43465 for ; Fri, 18 Sep 2020 17:28:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 00DCC21707 for ; Fri, 18 Sep 2020 17:28:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600450084; bh=ZGRDSjhooEhf1M6Kp2AFpnaYVcwgjGKPHfLW+5r9WsQ=; h=Date:From:To:Cc:Subject:List-ID:From; b=YZNQreJfybfo3adph2WH37ritOfukaL3hwQAAyLwZlLwZP0NidgwTsDEHtbnVrFgx Zchq1QBu2QccMLUsEVYSa4cJePIKgRCot1A49RaB4s7HPPN1LJuJp/py8yUUnLWoSu iGKCch5tt9G/0a666j9oWk3cxfv7ncrXk/wOVIxY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726298AbgIRR2D (ORCPT ); Fri, 18 Sep 2020 13:28:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55294 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726115AbgIRR2C (ORCPT ); Fri, 18 Sep 2020 13:28:02 -0400 Received: from mail-qt1-x833.google.com (mail-qt1-x833.google.com [IPv6:2607:f8b0:4864:20::833]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 81E94C0613CE for ; Fri, 18 Sep 2020 10:28:02 -0700 (PDT) Received: by mail-qt1-x833.google.com with SMTP id b2so5724046qtp.8 for ; Fri, 18 Sep 2020 10:28:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:mime-version :content-disposition; bh=HpgmTVIIkaIr3dSnikVjv7Tpc8Gx5M8NJIa6ariAHEw=; b=eR3SindTOzOE/HYpwlC4rPxH0J+/1FR2eXkGVhIaE7Y82Y13PeNvODp48JgW4VWykk Yiectqcq08xzhB8zkF7JUK5tULcZ3uCgqOJdDPj6FFCWqly+xJHVEIGeeP7ir5SKVzyP HCFtjTVjpBDhZmnpc7oWcJyivMAjcjCxI351uvx6lVukWrbOVJSfe2wY0aWIXM4CMkXQ p/qistFshUPtCsT0jor3S8STm/elfGgSNJNngK9ibEXgo4YVcj+v0wGWwoWJHsAhZvf2 OXMdwDinyLUQSjCvj+UGMp0Ao2IPde8WZQzZOGP3DiHBblOSCPhy4u0eoNLGlPqaYXmq /FhQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :mime-version:content-disposition; bh=HpgmTVIIkaIr3dSnikVjv7Tpc8Gx5M8NJIa6ariAHEw=; b=jXRaiUi9msxP4Yg7c3D+9EXTUzzo2W/IUHvwEHU9v1XfDkNH5uHr5lkCUySgosc8Le YM3VsQirOl/nfr5rhb4kumveNWNQvBMEDQJayZ+s5J24/qiX96t2Os+6e3pQERvbkRBF TaFd9BsdJsgPXySsTlb818r7m983M/OggfhEj+XFwcBtcDnMPfb+JIC9L8SRvFMfqxrN 92NxI1qgvdH+j+qLWCGzImbWXlTH/kCDNikWfTRju7ej+uUujutNIrSizxw4GG5B9+UC gjvJWfRSKasbUGzQC2H/VcjizUbcOVOCeg1C4bsP/lWa8yclIT0XPpU6bFqzgQGHGdZs Ewkg== X-Gm-Message-State: AOAM533tnZzC6SOSlJExAEmFQuGyiFjiwos/O72a8amULlViLdYEQgR7 BOEtidsF4f43XyemW0UBMGU= X-Google-Smtp-Source: ABdhPJwAz8e/yE636I1OD5gKWM1Sl6NqkwJtEDnW3uVFhVf47Kk10HfoD8zBobZxsfY5ql/mscV7rg== X-Received: by 2002:ac8:3836:: with SMTP id q51mr21827862qtb.41.1600450081614; Fri, 18 Sep 2020 10:28:01 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:602a]) by smtp.gmail.com with ESMTPSA id y73sm2437539qkb.23.2020.09.18.10.28.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2020 10:28:00 -0700 (PDT) Date: Fri, 18 Sep 2020 13:27:59 -0400 From: Tejun Heo To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Rik van Riel Subject: sched: rq->nr_iowait transiently going negative after the recent p->on_cpu optimization Message-ID: <20200918172759.GA4247@mtj.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Peter, I noticed /proc/stat::procs_blocked going U64_MAX transiently once in the blue moon without any other persistent issues. After looking at the code with Rik for a bit, the culprit seems to be c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu") - it changed where ttwu dec's nr_iowait and it looks like that can happen before the target task gets to inc. Thanks. -- tejun