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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5538C46467 for ; Wed, 11 Jan 2023 11:40:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232404AbjAKL21 (ORCPT ); Wed, 11 Jan 2023 06:28:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229688AbjAKL1V (ORCPT ); Wed, 11 Jan 2023 06:27:21 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5ED3112767 for ; Wed, 11 Jan 2023 03:27:02 -0800 (PST) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1673436419; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cnm+ywz+v6qAg22yzqr9Q3YUeRd4yzvHh7NAxESwhp4=; b=3zypZmkgtv2BCZJBB9H8rdZt67sWWh8uxbiehYqUFH/K0C21uZlrXjrSdDeveKtYf/y6LV ets4xWTVDiGMRz1AfUX7pTcnxhnc10JUn2FZfXgjQlNtI8BSng5oKtKH1B0xT71LL9SkF/ Bbpc8kpVNMDrjhW2BomJO14sYTOWRKCsveLepK2NirohTFi08GrslAybCTEVr/VycNgeD3 TD0TjIAshf25kvKWt+hMgorQZdjDVcYiZmR+xieAFT9r3VNyuXolJylBBE93/KjXH+jhot un9q+dy7i8IlfYhRyp+MOKbrcLDw4libuw5cGzIJE5OOdW5cCMFp1b14WuMRiw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1673436419; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cnm+ywz+v6qAg22yzqr9Q3YUeRd4yzvHh7NAxESwhp4=; b=Okp/ZW3/ZL8Lq4j9ot9ueLm8Kg/0R/8uGcrDj/jo5nQJf3wQFvZM4rtPz4MTkiIqzUkXQN dnO/JkcSUVmpymAA== To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org, ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com, Waiman Long , John Stultz , "Paul E . McKenney" Subject: Re: [PATCH clocksource 5/6] clocksource: Suspend the watchdog temporarily when high read latency detected In-Reply-To: <20230105010701.1773895-5-paulmck@kernel.org> References: <20230105010429.GA1773522@paulmck-ThinkPad-P17-Gen-1> <20230105010701.1773895-5-paulmck@kernel.org> Date: Wed, 11 Jan 2023 12:26:58 +0100 Message-ID: <87r0w1ia65.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 04 2023 at 17:07, Paul E. McKenney wrote: > This can be reproduced by running memory intensive 'stream' tests, > or some of the stress-ng subcases such as 'ioport'. > > The reason for these issues is the when system is under heavy load, the > read latency of the clocksources can be very high. Even lightweight TSC > reads can show high latencies, and latencies are much worse for external > clocksources such as HPET or the APIC PM timer. These latencies can > result in false-positive clocksource-unstable determinations. > > Given that the clocksource watchdog is a continual diagnostic check with > frequency of twice a second, there is no need to rush it when the system > is under heavy load. Therefore, when high clocksource read latencies > are detected, suspend the watchdog timer for 5 minutes. We should have enough heuristics in place by now to qualify the output of the clocksource watchdog as a random number generator, right?