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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 23914C43603 for ; Fri, 6 Dec 2019 17:12:47 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E34B820706 for ; Fri, 6 Dec 2019 17:12:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="fFIDUgKO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E34B820706 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41570 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idH9p-0002VY-HI for qemu-devel@archiver.kernel.org; Fri, 06 Dec 2019 12:12:45 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60276) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idFRn-0008DP-VU for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:23:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1idFRm-000785-Iq for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:23:11 -0500 Received: from mail-ot1-x344.google.com ([2607:f8b0:4864:20::344]:42031) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1idFRm-00075a-8o for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:23:10 -0500 Received: by mail-ot1-x344.google.com with SMTP id 66so6081470otd.9 for ; Fri, 06 Dec 2019 07:23:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lLL/PA8yye6H36YmDTDJ1uLtOzjPFZ9wMfmCB3T9Qaw=; b=fFIDUgKOI1eK6U6SOWpzPMY5IN6xLt9g7ESb8lserQJo4MEbirU+ui8SF1e4sw60+S E1Xf+J43b/F8q3V8NvBwVLwOIL+W1EsXSxY3Dc2H9NlwF6aeE470tJBYmDgrRTfeLvkF HFrAomGXZqDzHmZM+HrnhTUJ5UC5Z9v1YgiMUWq5mBdT9vUPGwE9emNaiP4EtNUwNi45 FwliZR36D0M1XhKbSPx3HbHNsiLnn40s84Yd8RL2ISNZhZW4RqPVCnakx+J9v3PeY33F mxlimG9lU9M5Jw4qT+gnRtXyt5g6zGUS2kYQaFu5E1f2aDM0Kv0AaSW8BLUBbh3XK6yb IpwQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lLL/PA8yye6H36YmDTDJ1uLtOzjPFZ9wMfmCB3T9Qaw=; b=ltjCEJcm/I3FhuOZaC1DB8Pe5amMQGm2pw2T8CDX9kg3823LxZynvNeCNYYEgHMmta Lz6/l7PZCOsIUTUZbnuXj3hv3+lGDpcs2MGPKLscLMXLhfD9gr6eW33Xi35ZP7cmW68R yT7HHsLkftd4A3yZ90oABwKlC8X08ejM5xur3nAxQ0xWcw4a74LJfbQRAVYCnvpgibox oLtocwv2YYyDlsBz0VPui2U6wf/Jxi69R9Hwf/ObcY+1kHzLkgd0Oz04RC2Or141s9bS +51TysZQJ8aUGFVvPw73EeztJdT/5tq2zgB0annJwprdxFXRLJkoHvDef41nVvGahYcZ f+YA== X-Gm-Message-State: APjAAAXAAekccDXBCsaxOnvD9GU4nJLaESQ0ANAW7434v+0jwkMoyEX8 uT9TNpPnujl36/pb9LlVQdAy5uO2dzeDUh0oCP86vA== X-Google-Smtp-Source: APXvYqw03zSH9ugAJHHK2drjDnpsWCs3dJY/2x/6anKkZgiejvRbtuCIpGjAyWmr6rs8oUwX7MlxyngqTAlyD4EoXlY= X-Received: by 2002:a9d:12d2:: with SMTP id g76mr11769992otg.232.1575645789270; Fri, 06 Dec 2019 07:23:09 -0800 (PST) MIME-Version: 1.0 References: <20191016143410.5023-1-drjones@redhat.com> In-Reply-To: <20191016143410.5023-1-drjones@redhat.com> From: Peter Maydell Date: Fri, 6 Dec 2019 15:22:58 +0000 Message-ID: Subject: Re: [PATCH v1 0/5] target/arm/kvm: Provide an option to adjust virtual time To: Andrew Jones Content-Type: text/plain; charset="UTF-8" X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::344 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marc Zyngier , qemu-arm , Richard Henderson , QEMU Developers , bijan.mottahedeh@oracle.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 16 Oct 2019 at 15:34, Andrew Jones wrote: > > v2: > - move from RFC status to v1 > - put kvm_arm_vm_state_change() in kvm.c to share among kvm32.c and kvm64.c > - add r-b's from Richard > > > This series is inspired by a series[1] posted by Bijan Mottahedeh about > a year ago. The problem described in the cover letter of [1] is easily > reproducible and some users would like to have the option to avoid it. > However the solution, which is to adjust the virtual counter offset each > time the VM transitions to the running state, introduces a different > problem, which is that the virtual and physical counters diverge. As > described in the cover letter of [1] this divergence is easily observed > when comparing the output of `date` and `hwclock` after suspending the > guest, waiting a while, and then resuming it. Because this different > problem may actually be worse for some users, unlike [1], the series > posted here makes the virtual counter offset adjustment optional and not > even enabled by default. Besides the adjustment being optional, this > series approaches the needed changes differently to apply them in more > appropriate locations. Finally, unlike [1], this series doesn't attempt > to measure "pause time" itself. Simply using QEMU_CLOCK_VIRTUAL, which > only ticks when the VM is not stopped, is sufficient. So I guess my overall question is "what is the x86 solution to this problem, and why is this all arm-specific?" It would also be helpful to know how it fits into all the other proposals regarding time in VMs. thanks -- PMM