From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751580AbdI1XJf (ORCPT ); Thu, 28 Sep 2017 19:09:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39214 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbdI1XJe (ORCPT ); Thu, 28 Sep 2017 19:09:34 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 2377E5D698 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=mtosatti@redhat.com Date: Thu, 28 Sep 2017 18:41:21 -0300 From: Marcelo Tosatti To: Paolo Bonzini Cc: Peter Zijlstra , Konrad Rzeszutek Wilk , mingo@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall\ Message-ID: <20170928214121.GA16169@amt.cnet> References: <20170923134114.qdfdegrd6afqrkut@hirez.programming.kicks-ass.net> <855950672.7912001.1506258344142.JavaMail.zimbra@redhat.com> <20170925025751.GB30813@amt.cnet> <20170925091316.bnwpiscs2bvpdxk5@hirez.programming.kicks-ass.net> <00ff8cbf-4e41-a950-568c-3bd95e155d4b@redhat.com> <20170926224925.GA9119@amt.cnet> <6f4afefd-8726-13ff-371e-0d3896b4cf6a@redhat.com> <20170928004452.GA30040@amt.cnet> <10635834-459a-9ec1-624d-febd6b5af243@redhat.com> <20170928213508.GA14053@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170928213508.GA14053@amt.cnet> User-Agent: Mutt/1.5.21 (2010-09-15) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 28 Sep 2017 23:09:34 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 28, 2017 at 06:35:08PM -0300, Marcelo Tosatti wrote: > On Thu, Sep 28, 2017 at 09:22:02AM +0200, Paolo Bonzini wrote: > > On 28/09/2017 02:44, Marcelo Tosatti wrote: > > >> Again: if you have many interruptions, it's not a flaw in KVM or QEMU's > > >> design, it's just that someone is doing something stupid. It could be > > >> the guest (e.g. unnecessary devices or daemons as in the example above), > > >> QEMU (e.g. the RTC emulation used to trigger QEMU timers twice a second > > >> just to increment the clock), or the management (e.g. polling "is the VM > > >> running" 50 times per second). But it can and must be fixed. > > > > > > No, i mean you can run anything in VCPU-0 (it is valid to do that). > > > And that "anything" can generate 1 interrupt per second, 1000 or 10.000 > > > interrupts per second. Which are all valid things to be done. > > > > > > "I can't run a kernel compilation on VCPU-0 because that will impact > > > latency on the realtime VCPU-1" is not acceptable. > > > > That shouldn't happen. Sources of frequent interruptions have all been > > fixed or moved outside the main thread. > > > > If there are more left, report the bug and we'll see how to fix it in > > userspace. > > > > Paolo > > What should not happen? The generation of 10.000 interrupts per second > (say disk IO completion) on a given workload ? Are you suggesting that, workloads in vcpu-0 should be limited in the number of interrupts (and durations of each interruption), so that the realtime vcpu-1's latency requirement is met ? I don't see how that suggestion can work because even if you make each exit small, the frequency of them will cause a latency violation on vcpu-1.