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 22B8DE8FDD1 for ; Wed, 4 Oct 2023 08:06:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241706AbjJDIGi (ORCPT ); Wed, 4 Oct 2023 04:06:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241587AbjJDIGg (ORCPT ); Wed, 4 Oct 2023 04:06:36 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BF90C83; Wed, 4 Oct 2023 01:06:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Bf/DwkEUdY4N5nesRCvh1+km/Cc8zVLg9CIGZn27uPw=; b=PBo3rbK34jPPs9/0BwPIk6pSwW 3IOkCc8URXU++w1It54k4oJjSNgRXP7nDu1XtC3uwK482zwLwSLkoGyJvt7Yu7Kj3Y6WWN3nyoQNH X5K1bs1NvQkFFlZYHFNlcGu6dCiJyCtM8LvkJp5bILAJSUJAezqXox48niMcOpYcF/Em/UgJWWMY2 Ayf7/KyjtC6g3qBUbmSMbzIIcMa4TtXzRNDYKR6uIuSy8g7ewAn6/A+RUAtvAHJ9FvBeAKkg0QgIU Egdnfakhyn5mG4IWD5miH02+NAqOvwy89drNsJxAn3UPUytM2MTQl9RfDP6MaAHBZMDbdrCxKY0e9 V6Aw1ZGA==; Received: from [2001:8b0:10b:5:3189:f402:1b52:3ed] (helo=u3832b3a9db3152.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qnwtb-002G6d-6R; Wed, 04 Oct 2023 08:06:15 +0000 Message-ID: Subject: Re: [PATCH RFC 1/1] KVM: x86: add param to update master clock periodically From: David Woodhouse To: Sean Christopherson Cc: Dongli Zhang , Joe Jin , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com Date: Wed, 04 Oct 2023 09:06:14 +0100 In-Reply-To: References: <20230926230649.67852-1-dongli.zhang@oracle.com> <377d9706-cc10-dfb8-5326-96c83c47338d@oracle.com> <36f3dbb1-61d7-e90a-02cf-9f151a1a3d35@oracle.com> <884aa233ef46d5209b2d1c92ce992f50a76bd656.camel@infradead.org> <52a3cea2084482fc67e35a0bf37453f84dcd6297.camel@infradead.org> <20EAA3C4-A9F4-4EC1-AE0C-D540CC2E024A@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-TBROPnPPfvY/7NJLtfAT" User-Agent: Evolution 3.44.4-0ubuntu2 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-TBROPnPPfvY/7NJLtfAT Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2023-10-03 at 17:07 -0700, Sean Christopherson wrote: >=20 > The issue is that the timekeeping code doesn't provide a notification mec= hanism > to *just* get updates for things like suspend/reume.=C2=A0 We could maybe= do something > in KVM like unregister the notifier if the TSC is constant, and manually = refresh > on suspend/resume.=C2=A0 But that's pretty gross too, and I'd definitely = be concerned > that we missed something. Or *in* the existing notifier, just do the maths (correctly!) and don't update KVM's raw_clock data if the only thing that's really changed is the passage of time? On the whole, it's better if your other patch works to avoid the drift in the first place. 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