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=-11.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 78523C4363A for ; Wed, 21 Oct 2020 23:48:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CDE82417D for ; Wed, 21 Oct 2020 23:48:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="TzGB+PcZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2507293AbgJUXsg (ORCPT ); Wed, 21 Oct 2020 19:48:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38690 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2408091AbgJUXsf (ORCPT ); Wed, 21 Oct 2020 19:48:35 -0400 Received: from mail-oo1-xc44.google.com (mail-oo1-xc44.google.com [IPv6:2607:f8b0:4864:20::c44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9D134C0613CE for ; Wed, 21 Oct 2020 16:48:35 -0700 (PDT) Received: by mail-oo1-xc44.google.com with SMTP id n2so977393ooo.8 for ; Wed, 21 Oct 2020 16:48:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=EUWpT0xSzb04KdW+F3F/7B/sEhkE2FW0IA92LIadnb8=; b=TzGB+PcZPJBYfA334G4mwAHms3nMJQgO5kBKCplD5ftTsIpzHst8Wc5qy2s4GmdU6y cTD6tBkz9zWLHCR5djxMlXNbxXIKc4cjaKSKiL2GNLfbVEguNaX3DCqNuO47Bw2vDmai YT1gMmrR2EQniWYS8Wurbon7JAUhBHTfxVx8tq+a3TFs4jqrl9maJUGKhlSOS9Uasxff Wo5HjQ64IZeDrU29Vu7dtcNtYAD0nLtQ9FP9BixRBFn/ATtcjTE/d2THfDZRjkP71DRU mX/Usmi4LdNK6g0+k/U9RUt0I3DXnB1Lz/FFSn1BI7mr4tgt2j2c1Yy2ophLt5R2ulcp LqzQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EUWpT0xSzb04KdW+F3F/7B/sEhkE2FW0IA92LIadnb8=; b=HG1tlx3DFcREeyaz8Lh0pTWRxsV4NKoD4gIQChX69AvP41aXlbtOwgnhEDuNEcVSpx LPcTPjIgtBhb0Riy5lub5etVqifRgwVH1XJiwu4cTCIBJA8LcSKe9PTVSbKKsay5GDT0 xU9rhvrhccxJCQ0wYp7ThXO+BKe1g1/rmAj071oN/kEpx2QqikV1mFQKGEXeIYJnPIXf BkInATwXF6fCKvNvsphjZKoLgELKeQhVzk1MCcUwd9FFcFpd0XTOmGVB4zxy7lLK7pKr u/D82agwnDqX3cscYomeBqVfVEpDHhhyPi9vx9FPHL/DjnUdRUURTd2XtgwYOt5KHLMo C0tg== X-Gm-Message-State: AOAM531/Di6Iko6kM7ZyqK2XUx9mESYT21hhqVBptUjUO0Q6R9giTqCd zu50Gs4JgDajqhxOGOiQd0WmTT0ntXRi2bsMA1KdOg== X-Google-Smtp-Source: ABdhPJyB2FC2rlEH1r9EaJUtkAHoI4Y4o5gBI6sfghZB+w+2PxHcuAUrRjnCcGgTMGQVK+lisMXcgkfNyAiId+kJ2TE= X-Received: by 2002:a4a:ce90:: with SMTP id f16mr22653oos.55.1603324114795; Wed, 21 Oct 2020 16:48:34 -0700 (PDT) MIME-Version: 1.0 References: <20201020205704.1741543-1-xii@google.com> <20201020205704.1741543-2-xii@google.com> <20201021101257.GC2628@hirez.programming.kicks-ass.net> In-Reply-To: <20201021101257.GC2628@hirez.programming.kicks-ass.net> From: Xi Wang Date: Wed, 21 Oct 2020 16:48:38 -0700 Message-ID: Subject: Re: [PATCH v2 1/1] sched: watchdog: Touch kernel watchdog with sched count To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Josh Don , LKML , Paul Turner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 21, 2020 at 3:13 AM Peter Zijlstra wrote: > > On Tue, Oct 20, 2020 at 01:57:04PM -0700, Xi Wang wrote: > > > + if (watchdog_touch_with_sched) { > > + /* Trigger reschedule for the next round */ > > + set_tsk_need_resched(current); > > + set_preempt_need_resched(); > > Blergh.. that's gross. This relies on this being in IRQ context and > either: PREEMPT=y *OR* this always being from userspace. Otherwise > there's no guarantee the return-from-interrupt will actually schedule. > Maybe I missed something but I think immediate rescheduling is not required? E.g. software watchdog should fire if there is a kernel busy loop and kernel preemption is not enabled. The current method ends up with a thread wakeup so there is no guaranteed reschedule either? -Xi