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_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 4A1D6C31E46 for ; Wed, 12 Jun 2019 09:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15BA92082C for ; Wed, 12 Jun 2019 09:38:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="OOwmIY2r" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408859AbfFLJiD (ORCPT ); Wed, 12 Jun 2019 05:38:03 -0400 Received: from mail-ot1-f67.google.com ([209.85.210.67]:42026 "EHLO mail-ot1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2408773AbfFLJiC (ORCPT ); Wed, 12 Jun 2019 05:38:02 -0400 Received: by mail-ot1-f67.google.com with SMTP id l15so14761009otn.9; Wed, 12 Jun 2019 02:38:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Uho8KQeGL4zvCiWfgtRd1WVA8bccWLCM5Olh/mEH/V0=; b=OOwmIY2ri3gcT6Pn+fQxfeU643IzNCgpBtnRsglxxb2zPUAual001NiYqq/PxS14Mc VyTziLa+0CSKtERPDlbeOg06mcYorg002XRe8tnfyg/NA2MJisNk8exLFcgFWDrjKt+6 /fK6XrJcD1yRTwCDZSScrRr/3GGZuYW+702rI3lYUYDFLmWpwtnfgy2QDWoaGS+gF+w8 cPyNi+22wC2rTiDqOqVOmVtc3N0HHOSKDNrEFvSrSofxkfJSsS4geeZz13fvkz/PT6K4 d/2NIHDSW11AnMZ6dLSo9ZG3Mfl/f/fpsM4D0CmWCx7QhKReApTWg8gYlHqa8o6osrNi nIoQ== 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=Uho8KQeGL4zvCiWfgtRd1WVA8bccWLCM5Olh/mEH/V0=; b=S9a38cjwPobNPRzLRwapOsMOfdQYNadFlY+ovquRe5tcA7ImWGPmG+D074SvUXBKjv bn4JpKO/EAQyHkI4WeOmqTLB/f9TEkYkkgBszRas/3wiKiFTv5OB80H8aJlw6DC760EM hS8+qOXWGivvV7lkemcXTNAuEAH8AfCpEfrZBeHbAtxyDUkFMys6ZPqMNLm1XssCgmhN bWFVZ0Rtl435hcdxZ13eiBcv9u5I4Li/tdmXqSDHnvexj5fl1lHC73MLg8qFobvMwqqD FYJ99JdjQSDA6x/IQBKrqhf1I9Vb9EbDEN9QP+PH9Ag0lEHRSMD6dxqhwuL64dGNE94n LY5w== X-Gm-Message-State: APjAAAVyU21c1wKTWbrd0/wH/upcYx/lOEz6o2+ekYrQUlQGid2Kex6K swo+qM4FOUr6pJaPU8ipZmpX3Anx4D7imRuygsY= X-Google-Smtp-Source: APXvYqxS6QKBxt7vLOAsARJg20qqX12U2VOEM9zQ24quttGdwmW1DulmY3Xq3y4pTVI85hKXWEgARZZlxuJmjXjSmP8= X-Received: by 2002:a9d:7601:: with SMTP id k1mr1632240otl.254.1560332282293; Wed, 12 Jun 2019 02:38:02 -0700 (PDT) MIME-Version: 1.0 References: <1558585131-1321-1-git-send-email-wanpengli@tencent.com> <20190530193653.GA27551@linux.intel.com> <754c46dd-3ead-2c27-1bcc-52db26418390@redhat.com> In-Reply-To: <754c46dd-3ead-2c27-1bcc-52db26418390@redhat.com> From: Wanpeng Li Date: Wed, 12 Jun 2019 17:38:45 +0800 Message-ID: Subject: Re: [PATCH 1/2] KVM: LAPIC: Optimize timer latency consider world switch time To: Paolo Bonzini Cc: Sean Christopherson , LKML , kvm , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 31 May 2019 at 17:01, Paolo Bonzini wrote: > > On 30/05/19 21:36, Sean Christopherson wrote: > >> +u32 __read_mostly vmentry_lapic_timer_advance_ns = 0; > >> +module_param(vmentry_lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); > > Hmm, an interesting idea would be to have some way to "lock" this param, > > e.g. setting bit 0 locks the param. That would allow KVM to calculate the > > cycles value to avoid the function call and the MUL+DIV. If I'm not > > mistaken, vcpu->arch.virtual_tsc_khz is set only in kvm_set_tsc_khz(). > > I would just make it read-only. But I'm afraid we're entering somewhat > dangerous territory. There is a risk that the guest ends up entering > the interrupt handler before the TSC deadline has actually expired, and > there would be no way to know what would happen; even guest hangs are > possible. Agreed, do it in v3. Regards, Wanpeng Li