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 4C939C433F5 for ; Wed, 17 Nov 2021 21:57:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B7A661A07 for ; Wed, 17 Nov 2021 21:57:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240983AbhKQWAH (ORCPT ); Wed, 17 Nov 2021 17:00:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:25495 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241276AbhKQV6x (ORCPT ); Wed, 17 Nov 2021 16:58:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637186152; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=H6VIrXJQXepYyEy6GUgX2mEjRrDCUS7p7t5J+28qOmg=; b=cAGfytzxugxZPZmaJ1fL05DDlr9VmiA2K0YNk6e12UrdL5+BXuoSohPDjvLgYO9ao6vSLZ BNSWy6eORbB2GRjfcGvfzObg7vLOr3aTPAHcEZX5ydjsI9AQeTBO35EuKDJXSDTralp+DO 9Ja2gGm6HVElHd4Tvaj5DL+uJA8BfSU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-472-kj9fOSGANyiZmjwZBtjywQ-1; Wed, 17 Nov 2021 16:55:48 -0500 X-MC-Unique: kj9fOSGANyiZmjwZBtjywQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AF5EA57051; Wed, 17 Nov 2021 21:55:46 +0000 (UTC) Received: from [10.22.33.89] (unknown [10.22.33.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id A04E15C22B; Wed, 17 Nov 2021 21:55:45 +0000 (UTC) Message-ID: Date: Wed, 17 Nov 2021 16:55:45 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v2 0/4] clocksource: Avoid incorrect hpet fallback Content-Language: en-US To: paulmck@kernel.org Cc: John Stultz , Thomas Gleixner , Stephen Boyd , Feng Tang , linux-kernel@vger.kernel.org, Peter Zijlstra , Cassio Neri , Linus Walleij , Frederic Weisbecker References: <20211116234426.837799-1-longman@redhat.com> <20211117165426.GG641268@paulmck-ThinkPad-P17-Gen-1> <7cb5ab62-21ea-f649-2009-38b8c1ff283a@redhat.com> <20211117212547.GO641268@paulmck-ThinkPad-P17-Gen-1> From: Waiman Long In-Reply-To: <20211117212547.GO641268@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/17/21 16:25, Paul E. McKenney wrote: > On Wed, Nov 17, 2021 at 01:51:51PM -0500, Waiman Long wrote: >> On 11/17/21 11:54, Paul E. McKenney wrote: >>> On Tue, Nov 16, 2021 at 06:44:22PM -0500, Waiman Long wrote: >>> A few questions: >>> >>> 1. Once you have all the patches in place, is the increase in >>> WATCHDOG_MAX_SKEW from 50us to 100us necessary? >> I think so. Using Feng's reproducer, I was able to cause a hpet-hpet delay >> of more than 90us on a 1-socket system. With a default 50us >> WATCHDOG_MAX_SKEW, the chance of a warning showing up will be much higher. >> Trying to minimize the chance that a warning may appear is my primary reason >> to increase WATCHDOG_MAX_SKEW. > Should we downgrade the "had to retry read" complain to pr_info(), > and make the only real warning be the case where a large number of > consecutive read attempts fail? I believe that Heiner Kallweit was > looking for something like this. Sure. I will downgrade it to pr_info(). > >>> 2. The reason for having cs->uncertainty_margin set to >>> 2*WATCHDOG_MAX_SKEW was to allow for worst-case skew from both >>> the previous and the current reading. Are you sure that >>> dropping back to WATCHDOG_MAX_SKEW avoids false positives? >> I can remove the hunk of changing cs->uncertainty_margin. It is critical for >> this patch. > Assuming "not critical", good! Yes, it is "not critical". Somehow I missed the "not" :-) Cheers, Longman