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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 D6A5DC433FF for ; Wed, 14 Aug 2019 12:50:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEDA52083B for ; Wed, 14 Aug 2019 12:50:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727807AbfHNMuE (ORCPT ); Wed, 14 Aug 2019 08:50:04 -0400 Received: from mail-wm1-f68.google.com ([209.85.128.68]:35495 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727671AbfHNMuE (ORCPT ); Wed, 14 Aug 2019 08:50:04 -0400 Received: by mail-wm1-f68.google.com with SMTP id l2so4361035wmg.0 for ; Wed, 14 Aug 2019 05:50:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:openpgp:message-id :date:user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=nIdOkJj+NCHUIyznIs60RDyt0NVOMuTgVRbV4NbgyKw=; b=tgxE4k9lg/Zer3SBL23RdN/ky/KQVpaYv1IKO9T1Fx1ByDLJPMiD70BH86w9zNxU0h yv/1nc+ncMd3ghoVkp3i7Kw4kJX4AURVzL1kCn9PYx3s8HaMX6BTwxAtxsVECeZtBCFP 1IVWYEqmKjZgdAGQ/k7ZVf/nTM+b0LTpBE9lT33ioBHX7gWjGWpkqG1NFUnEwvoDuOht wl8CCeHyNbg4ZEwFSLs4NrrsALvWzLLIDXfEMB41pEt6GSkMbRk7qxzukGojfgPNT7ve XbTeESwW/rh0j6J9i80QinWllGut2i+dSaeJ4qOdJwGrKkAnosUuLeVWFZ9pgaULTLdR 8KrQ== X-Gm-Message-State: APjAAAVFc+B6xBVX3VcyX0JW3qXNOWZzQ0WPEui6tbWj8pz1hWEEHzlo vYHTTuKQplJRYn2U9yLXl1L1Cw== X-Google-Smtp-Source: APXvYqy8MiEEUjvq7rGAdJGFImOXcGnh48g6y3RN2Di3ehrfNAs3jeflNUzl79F84DuabN//PnQOaQ== X-Received: by 2002:a7b:c8cb:: with SMTP id f11mr8440647wml.138.1565787002603; Wed, 14 Aug 2019 05:50:02 -0700 (PDT) Received: from [192.168.10.150] ([93.56.166.5]) by smtp.gmail.com with ESMTPSA id f17sm4210265wmj.27.2019.08.14.05.50.01 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Wed, 14 Aug 2019 05:50:02 -0700 (PDT) Subject: Re: [PATCH] KVM: LAPIC: Periodically revaluate appropriate lapic_timer_advance_ns To: Wanpeng Li Cc: LKML , kvm , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <1565329531-12327-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: Date: Wed, 14 Aug 2019 14:50:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/08/19 11:06, Wanpeng Li wrote: > On Fri, 9 Aug 2019 at 18:24, Paolo Bonzini wrote: >> >> On 09/08/19 07:45, Wanpeng Li wrote: >>> From: Wanpeng Li >>> >>> Even if for realtime CPUs, cache line bounces, frequency scaling, presence >>> of higher-priority RT tasks, etc can cause different response. These >>> interferences should be considered and periodically revaluate whether >>> or not the lapic_timer_advance_ns value is the best, do nothing if it is, >>> otherwise recaluate again. >> >> How much fluctuation do you observe between different runs? > > Sometimes can ~1000 cycles after converting to guest tsc freq. Hmm, I wonder if we need some kind of continuous smoothing. Something like if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) { /* no update for random fluctuations */ return; } if (unlikely(timer_advance_ns > 5000)) timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; apic->lapic_timer.timer_advance_ns = timer_advance_ns; and removing all the timer_advance_adjust_done stuff. What do you think? Paolo