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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B0BA2C7618B for ; Mon, 29 Jul 2019 10:59:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8DC0821655 for ; Mon, 29 Jul 2019 10:59:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387543AbfG2K7a (ORCPT ); Mon, 29 Jul 2019 06:59:30 -0400 Received: from mail-wm1-f67.google.com ([209.85.128.67]:39076 "EHLO mail-wm1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387424AbfG2K7a (ORCPT ); Mon, 29 Jul 2019 06:59:30 -0400 Received: by mail-wm1-f67.google.com with SMTP id u25so42686804wmc.4 for ; Mon, 29 Jul 2019 03:59:28 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=ZofcKDycB29XhDLuv66ThbXp2pcFI/cJTwXP21ke4VY=; b=SGsICIkqW7Vf099EvOe8kfKjqr7WsNio+xUj5WqAyl81Y0YsSAIWzNQ91lhuikYzlW q4WFo8SRra6AmOD6Q6Mz8WEGbeyx+H6D3RkyWZE8dExpLhIORuUvD84GR9tQH5BXhVlV pqSFD0fjj/sJoFHfsQgjY0Dw2xF1asnbC9S+zPXqgYkTqhGhvlCP1GQ+GDHkjzo82Yqp gnOF6bCqMPEfoVTkOjSjExJt7Wcoz7EpR6xrh1Nvqes7zYATwXGvhzcG5ra2hX0d8iRN F7iI8b3fgr/krtR6dJuxa0IYkb/WgNhE5Py4BbrGUVewMv1bGqLowYqU3lrmnGcIzPO0 tVow== X-Gm-Message-State: APjAAAUwPbNnODnNMFD3JQfRMqJ5tz14vfXzuV1Gh3VN+8uGkVhPqVC0 6I2ugB3fyJod4FYpgF5Z5ukOLQ== X-Google-Smtp-Source: APXvYqz9v8tCt46RmejEdVRBDjbdRLOyKVUpwyHmlB+2XfNpS4AtquhMMTujdQfnT/E1zDJNlBGawA== X-Received: by 2002:a1c:9e90:: with SMTP id h138mr102770113wme.67.1564397968266; Mon, 29 Jul 2019 03:59:28 -0700 (PDT) Received: from vitty.brq.redhat.com (nat-pool-brq-t.redhat.com. [213.175.37.10]) by smtp.gmail.com with ESMTPSA id o126sm56535812wmo.1.2019.07.29.03.59.26 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 29 Jul 2019 03:59:27 -0700 (PDT) From: Vitaly Kuznetsov To: lantianyu1986@gmail.com Cc: Tianyu Lan , linux-arch@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, sashal@kernel.org, daniel.lezcano@linaro.org, arnd@arndb.de, michael.h.kelley@microsoft.com, ashal@kernel.org Subject: Re: [PATCH 0/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function In-Reply-To: <20190729075243.22745-1-Tianyu.Lan@microsoft.com> References: <20190729075243.22745-1-Tianyu.Lan@microsoft.com> Date: Mon, 29 Jul 2019 12:59:26 +0200 Message-ID: <87zhkxksxd.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org lantianyu1986@gmail.com writes: > From: Tianyu Lan > > Hyper-V guests use the default native_sched_clock() in pv_ops.time.sched_clock > on x86. But native_sched_clock() directly uses the raw TSC value, which > can be discontinuous in a Hyper-V VM. Add the generic hv_setup_sched_clock() > to set the sched clock function appropriately. On x86, this sets > pv_ops.time.sched_clock to read the Hyper-V reference TSC value that is > scaled and adjusted to be continuous. Hypervisor can, in theory, disable TSC page and then we're forced to use MSR-based clocksource but using it as sched_clock() can be very slow, I'm afraid. On the other hand, what we have now is probably worse: TSC can, actually, jump backwards (e.g. on migration) and we're breaking the requirements for sched_clock(). -- Vitaly