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 4A212C2D0BF for ; Tue, 10 Dec 2019 11:49:37 +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 179E32073B for ; Tue, 10 Dec 2019 11:49:37 +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="tE2Bm7qH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 179E32073B 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]:55664 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iee1I-00045P-5G for qemu-devel@archiver.kernel.org; Tue, 10 Dec 2019 06:49:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33523) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iee0Z-0003YS-KQ for qemu-devel@nongnu.org; Tue, 10 Dec 2019 06:48:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iee0Y-0006qN-EH for qemu-devel@nongnu.org; Tue, 10 Dec 2019 06:48:51 -0500 Received: from mail-ot1-x344.google.com ([2607:f8b0:4864:20::344]:35061) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1iee0Y-0006pT-8I for qemu-devel@nongnu.org; Tue, 10 Dec 2019 06:48:50 -0500 Received: by mail-ot1-x344.google.com with SMTP id o9so15233614ote.2 for ; Tue, 10 Dec 2019 03:48:49 -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=SfXh7eKZqdpO2LGEgz3P0HSgLknLGqn+asJn+CHcrPI=; b=tE2Bm7qH6GjY2mQXj1MWvgEieR2tcKUidD2+T4ja754WnhBE5poHvZhfvZk96rQ5S2 ot2BaTtcY3DY42tK0z50hv406f57UoY7CIRrVDAwSk7/+YmaqNynl8/s0807+AgmdMcN qeKd5mpmh42vcCbxaUjAGhnzH+Fyp2gcCkdi9bAIAHhg+LdQd1EwriUvZeRcmZ1YteRK tlb/ayBCDE1x3f4pJyCP/RXMcyH7YTwW2dU5RF5ec/8ws3xgfU72zeJqC41XuS6IuSI/ KwF0F7NrVQc+czEmGXwgkIIL9YLUS2x1tu6eu6kBkzMN9shDKY8aYc3+91OXMdGyoYFA MhhQ== 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=SfXh7eKZqdpO2LGEgz3P0HSgLknLGqn+asJn+CHcrPI=; b=cZKk8Z/T12E5C373+JopOI/wtkqVccDHzvNnPMAyt3mqVDKJAIbwvPP9JdzBNqjB9o 2ZD5LKhrnCK1d/9ERgEA6hIS9hXiet80QGDU14RmDklEqqVf+4ZSk9aHOntWgNdpiJtI 2IsVJ+HgqHg/1D8mkp+EbmxY+hcPC8ymaYv1Y8D3uufhaB07R5oAilQuicUhexB+IHSy 8myVbsOND/kHRoRjCEJcqFfqqghfEE76nmFtkJRX6bKS9s3JTKiOC7mcyOwtEgOZ48hT iq02nGJ4d1B9D/mEz9AXmvOSrbfNDV7D4ccq3QBhQBr5CyvKC6KNuOJAUuowGcyU8+Id lS/g== X-Gm-Message-State: APjAAAUfHZn8aaCZkaVy/1BsF5csACoun6YKDWpQikyAZY7KAuWbsRm4 yiyG1QrOCrzNt5Iyp9q/JEcbm9gaPFlXQA4NlOCueQ== X-Google-Smtp-Source: APXvYqx16K1ZVv4gv8fQvB3f5jY1DQINqwMflWH7jrq9BnIDUnmN6ak6Qlo+A9+K9Zeo9StUIhpvspJu/yxV93Rchq8= X-Received: by 2002:a9d:4d8a:: with SMTP id u10mr10486979otk.232.1575978529096; Tue, 10 Dec 2019 03:48:49 -0800 (PST) MIME-Version: 1.0 References: <20191016143410.5023-1-drjones@redhat.com> <20191206155327.7adiyjjkjh56mg2t@kamzik.brq.redhat.com> <596d07e933cb4da48dbba5b492e81a2438e78a2f.camel@redhat.com> <20191210110531.psjzlikir2ep2omo@kamzik.brq.redhat.com> In-Reply-To: <20191210110531.psjzlikir2ep2omo@kamzik.brq.redhat.com> From: Peter Maydell Date: Tue, 10 Dec 2019 11:48:38 +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: bijan.mottahedeh@oracle.com, Marc Zyngier , Richard Henderson , QEMU Developers , Andrea Bolognani , qemu-arm Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 10 Dec 2019 at 11:05, Andrew Jones wrote: > x86 developers could easily add this feature if/when they need a way to > disable their current default behavior. But, since the kvm-adjvtime > default would likely be 'on' for them, then they'd probably prefer the > feature be named kvm-no-adjvtime, and default 'off'. Should we try to > anticipate what x86 might want when naming this feature? IMO, we should > not, especially because I'm doubtful that x86 will ever want to implement > it. Also, what about the other KVM capable architectures? Which defaults > do they have now? And do we expect them to want to expose a switch to the > user to change it? My perspective here is mostly that I don't really understand the ins and outs of KVM and in particular handling of time in VMs, beyond knowing that it's complicated. So I prefer approaches that push back to "do everything the same for all architectures rather than having something that's arm-specific", because then things get more review from the larger mass of non-arm KVM/QEMU developers. Arm-specific switches/interfaces/designs just make arm more of a special-snowflake. I don't really have a basis to be able to review the patchset beyond those general biases. thanks -- PMM