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=-7.2 required=3.0 tests=BAYES_00,DATE_IN_PAST_03_06, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 58502C64E7A for ; Tue, 1 Dec 2020 19:29:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE6542151B for ; Tue, 1 Dec 2020 19:29:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZTCpMypN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731319AbgLAT3M (ORCPT ); Tue, 1 Dec 2020 14:29:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:58052 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731304AbgLAT3L (ORCPT ); Tue, 1 Dec 2020 14:29:11 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606850865; 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=hI2FKlF+kmqq5U4eXXUNmC/tjs6qqn+NATtqfedJVV4=; b=ZTCpMypNQhVjHFuzVZYIB1aJxig0T0dguFscNgC2+WKv92aOmRfvLxpFTzMvl3kaBsljUZ WEIyd3oUWOgJhKgaJnO+dwnlAEC6eFHWnzPakcQaCmKi2AyeOBJPZKwXc+tZWyDXgALc7G 4CykMRHZmSIF8Dc5SnAImLfsEw8uecE= 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-238-a1fetJ5wMZaJDqwTxXf4jg-1; Tue, 01 Dec 2020 14:27:43 -0500 X-MC-Unique: a1fetJ5wMZaJDqwTxXf4jg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1EEC1100E421; Tue, 1 Dec 2020 19:27:40 +0000 (UTC) Received: from fuller.cnet (ovpn-112-6.gru2.redhat.com [10.97.112.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0E45E9CA0; Tue, 1 Dec 2020 19:27:39 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id B9D804172EDC; Tue, 1 Dec 2020 12:02:05 -0300 (-03) Date: Tue, 1 Dec 2020 12:02:05 -0300 From: Marcelo Tosatti To: Thomas Gleixner Cc: Maxim Levitsky , kvm@vger.kernel.org, Paolo Bonzini , Oliver Upton , Ingo Molnar , Sean Christopherson , open list , Jonathan Corbet , Wanpeng Li , Borislav Petkov , Jim Mattson , "H. Peter Anvin" , "open list:DOCUMENTATION" , Joerg Roedel , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Vitaly Kuznetsov Subject: Re: [PATCH 0/2] RFC: Precise TSC migration Message-ID: <20201201150205.GA42117@fuller.cnet> References: <20201130133559.233242-1-mlevitsk@redhat.com> <20201130191643.GA18861@fuller.cnet> <877dq1hc2s.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877dq1hc2s.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 01, 2020 at 02:48:11PM +0100, Thomas Gleixner wrote: > On Mon, Nov 30 2020 at 16:16, Marcelo Tosatti wrote: > >> Besides, Linux guests don't sync the TSC via IA32_TSC write, > >> but rather use IA32_TSC_ADJUST which currently doesn't participate > >> in the tsc sync heruistics. > > > > Linux should not try to sync the TSC with IA32_TSC_ADJUST. It expects > > the BIOS to boot with synced TSCs. > > That's wishful thinking. > > Reality is that BIOS tinkerers fail to get it right. TSC_ADJUST allows > us to undo the wreckage they create. > > Thanks, > > tglx Have not seen any multicore Dell/HP systems require that. Anyway, for QEMU/KVM it should be synced (unless there is a bug in the sync logic in the first place).