From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v7 2/3] KVM: x86: trace mmio begin and complete Date: Tue, 04 Sep 2012 12:06:42 +0800 Message-ID: <50457E52.1070702@linux.vnet.ibm.com> References: <1346061106-5364-1-git-send-email-haodong@linux.vnet.ibm.com> <1346061106-5364-3-git-send-email-haodong@linux.vnet.ibm.com> <50448F72.80702@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Dong Hao , acme@infradead.org, mtosatti@redhat.com, mingo@elte.hu, linux-kernel@vger.kernel.org, kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from e23smtp07.au.ibm.com ([202.81.31.140]:35607 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750778Ab2IDEGz (ORCPT ); Tue, 4 Sep 2012 00:06:55 -0400 Received: from /spool/local by e23smtp07.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 4 Sep 2012 14:05:14 +1000 In-Reply-To: <50448F72.80702@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/03/2012 07:07 PM, Avi Kivity wrote: > On 08/27/2012 12:51 PM, Dong Hao wrote: >> From: Xiao Guangrong >> >> 'perf kvm stat record/report' will use kvm_exit and kvm_mmio(read...) to >> calculate mmio read emulated time for the old kernel, in order to trace >> mmio read event more exactly, we add kvm_mmio_begin to trace the time when >> mmio read begins, also, add kvm_io_done to trace the time when mmio/pio is >> completed >> > > Why is this so critical? > > If a lot of time is spent in in-kernel mmio, then 'perf top' will report > it. Otherwise the time between kvm_exit and kvm_entry describes the > time spent in the host. Not all of it is mmio handling, but it is quite > close. I have done some test, the new events can get more exact result, this is a example in my slides: the event handled time calculated by old events is: 0.000066(s) calculated by new events, the result is: 0.000005(s). So, i think it is worth introducing these new events. But if you do not care it or think these events are duplicate with current events or unmaintainable, i do not have strong opinion on that. Please let me know, i will drop them in the next version.