Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752303AbdLNNBZ (ORCPT ); Thu, 14 Dec 2017 08:01:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46852 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbdLNNBY (ORCPT ); Thu, 14 Dec 2017 08:01:24 -0500 Subject: Re: [PATCH RFC 0/7] kvm pvtimer To: Quan Xu , Konrad Rzeszutek Wilk Cc: Radim Krcmar , Yang Zhang , kvm , LKML , Ben Luo References: <1512722390-3654-1-git-send-email-quan.xu0@gmail.com> <20171208151014.GE12069@x230.dumpdata.com> <20171213162800.GS10097@char.us.oracle.com> <78ebabd2-cc38-2694-b104-c5e0230aba15@redhat.com> <7aef193f-900d-e8b1-35f7-2373ffdfa147@gmail.com> From: Paolo Bonzini Message-ID: <53430f19-2fd3-78cd-d45d-0ebb0a67e226@redhat.com> Date: Thu, 14 Dec 2017 14:00:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <7aef193f-900d-e8b1-35f7-2373ffdfa147@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 14 Dec 2017 13:01:24 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1204 Lines: 31 On 14/12/2017 13:06, Quan Xu wrote: > > > On 2017/12/14 19:56, Paolo Bonzini wrote: >> On 13/12/2017 17:28, Konrad Rzeszutek Wilk wrote: >>> 1) VM idle path and network req/resp services: >>> >>> Does this go away if you don't hit the idle path? Meaning if you >>> loop without hitting HLT/MWAIT? I am assuming the issue you are facing >>> is the latency - that is first time the guest comes from HLT and >>> responds to the packet the latency is much higher than without? >>> >>> And the arming of the timer? >>> 2) process context switches. >>> >>> Is that related to the 1)? That is the 'schedule' call and the process >>> going to sleep waiting for an interrupt or timer? >>> >>> This all sounds like issues with low-CPU usage workloads where you >>> need low latency responses? >> Even high-CPU usage, as long as there is a small idle time.  The cost of >> setting the TSC deadline timer twice is about 3000 cycles. >> >> However, I think Amazon's approach of not intercepting HLT/MWAIT/PAUSE >> can recover most of the performance and it's way less intrusive. > > Paolo, could you share the Amazon's patch or the LML link? thanks. Here: https://www.spinics.net/lists/kvm/msg159356.html Paolo