From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 1/3] KVM: trace mmio read event properly Date: Tue, 17 Jan 2012 10:36:37 +0800 Message-ID: <4F14DEB5.6020902@linux.vnet.ibm.com> References: <4F13EE3D.2070602@linux.vnet.ibm.com> <4F13EE73.1080504@linux.vnet.ibm.com> <4F13F967.5000007@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM To: Avi Kivity Return-path: In-Reply-To: <4F13F967.5000007@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 01/16/2012 06:18 PM, Avi Kivity wrote: > On 01/16/2012 11:31 AM, Xiao Guangrong wrote: >> In current code, we use KVM_TRACE_MMIO_READ to trace mmio read event which >> only can be completed immediately, instead of it, we trace the time when >> read event occur, then cooperate with then later patch, we can know the time >> of mmio read emulation >> >> @@ -3744,6 +3740,8 @@ mmio: >> /* >> * Is this MMIO handled locally? >> */ >> + trace_kvm_mmio(write ? KVM_TRACE_MMIO_WRITE : KVM_TRACE_MMIO_READ, > > It's better to push the conditional to the trace event itself, so it's > only evaluated if tracing is enabled. > Yes. >> + bytes, gpa, *(u64 *)val); > > We get the wrong value for reads here, no? > Yes, the value is meaningless in this point. > Can't we leave the code as is, and infer the start of the event from the > last kvm_exit trace? Yes, we can do it, but the same problems is we need trace vcpu id to get its vmexit, i will do it in the next version if you like this way :)