From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751984AbdJFOUJ (ORCPT ); Fri, 6 Oct 2017 10:20:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50970 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751616AbdJFOUG (ORCPT ); Fri, 6 Oct 2017 10:20:06 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 965592CE942 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=rkrcmar@redhat.com Date: Fri, 6 Oct 2017 16:20:03 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Wanpeng Li Cc: "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , Wanpeng Li Subject: Re: [PATCH v5 3/3] KVM: LAPIC: Apply change to TDCR right away to the timer Message-ID: <20171006142003.GB16459@flask> References: <1507214117-2899-1-git-send-email-wanpeng.li@hotmail.com> <20171005181427.GB5656@flask> <20171006130318.GA16459@flask> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 06 Oct 2017 14:20:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2017-10-06 22:03+0800, Wanpeng Li: > 2017-10-06 21:03 GMT+08:00 Radim Krčmář : > > 2017-10-06 07:14+0800, Wanpeng Li: > >> 2017-10-06 2:14 GMT+08:00 Radim Krčmář : > >> > 2017-10-05 07:35-0700, Wanpeng Li: > >> >> From: Wanpeng Li > >> >> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now); > >> >> + if (ktime_to_ns(remaining) < 0) > >> >> + remaining = 0; > >> >> + delta = mod_64(ktime_to_ns(remaining), apic->lapic_timer.period); > >> >> + > >> >> + if (!delta) > >> >> + return false; > >> >> + > >> >> + apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT) > >> >> + * APIC_BUS_CYCLE_NS * apic->divide_count; > >> > > >> > I'd prefer to apply the rate limiting (done earlier in this function) to > >> > the period. This version allows the guest to configure 128 times more > >> > frequent interrupts in the host. > >> > (And thinking about it, the version of [2/3] I proposed has similar > >> > problem when switching from one-shot to periodic, only there it is > >> > unpredictably limited by the speed of KVM.) > >> > >> We didn't stop and restart the timer, why the rate will influence us for [2/3]? > > > > It is because of the rate limiting -- the guest could setup a one-shot > > timer with a short expiration and switch to periodic > > Yeah, in addition, I think configure 128 means more slower interrupts > instead of faster. Yes, it says how many cycles it takes to decrement APIC_TMCCT. (I only concerned about the case where rate limit was configured with divide_count=128 and then switched to 1.)