From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Date: Tue, 17 Apr 2012 06:26:49 +0000 Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault Message-Id: <4F8D0D29.9050009@linux.vnet.ibm.com> List-Id: References: <4F742951.7080003@linux.vnet.ibm.com> <4F82E04E.6000900@redhat.com> <20120409175829.GB21894@amt.cnet> <4F8329D3.7000605@gmail.com> <20120409194614.GB23053@amt.cnet> <4F840DD2.3090101@redhat.com> <20120410204031.ffb5b976225ac9fe6dae474e@gmail.com> <4F842074.1050108@linux.vnet.ibm.com> <20120411211514.35db29c11460516e604059b6@gmail.com> <4F857B61.9080602@linux.vnet.ibm.com> <20120411231441.9d0984672dd252b806f99128@gmail.com> <20120413232528.c5ddbddb3cc0870d6e85a332@gmail.com> <4F8A95CB.9070104@redhat.com> <20120417004935.a9a39d951b3c24588e29edd2@gmail.com> In-Reply-To: <20120417004935.a9a39d951b3c24588e29edd2@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Takuya Yoshikawa Cc: Avi Kivity , kvm-ppc@vger.kernel.org, Marcelo Tosatti , Xiao Guangrong , LKML , KVM On 04/16/2012 11:49 PM, Takuya Yoshikawa wrote: > Although O(1) is actually O(1) for GET_DIRTY_LOG thread, it adds some > overheads to page fault handling. We may need to hold mmu_lock for properly > handling O(1)'s write protection and ~500 write protections will not be so > cheap. And there is no answer to the question how to achive slot-wise write > protection. > Actually no. We do not increase the overload on page fault for migration. The number of page fault of O(1) is the same as write-protect all spte. And, we can also avoid to hold mmu_lock to write-protect PML4s, we can use a generation number, and notify mmu to update its page table when dirty-log is enabled. Anyway, no performance data, no truth. Let me implement it first. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault Date: Tue, 17 Apr 2012 14:26:49 +0800 Message-ID: <4F8D0D29.9050009@linux.vnet.ibm.com> References: <4F742951.7080003@linux.vnet.ibm.com> <4F82E04E.6000900@redhat.com> <20120409175829.GB21894@amt.cnet> <4F8329D3.7000605@gmail.com> <20120409194614.GB23053@amt.cnet> <4F840DD2.3090101@redhat.com> <20120410204031.ffb5b976225ac9fe6dae474e@gmail.com> <4F842074.1050108@linux.vnet.ibm.com> <20120411211514.35db29c11460516e604059b6@gmail.com> <4F857B61.9080602@linux.vnet.ibm.com> <20120411231441.9d0984672dd252b806f99128@gmail.com> <20120413232528.c5ddbddb3cc0870d6e85a332@gmail.com> <4F8A95CB.9070104@redhat.com> <20120417004935.a9a39d951b3c24588e29edd2@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , kvm-ppc@vger.kernel.org, Marcelo Tosatti , Xiao Guangrong , LKML , KVM To: Takuya Yoshikawa Return-path: Received: from e23smtp01.au.ibm.com ([202.81.31.143]:46062 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751932Ab2DQG1H (ORCPT ); Tue, 17 Apr 2012 02:27:07 -0400 Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 17 Apr 2012 06:19:21 +1000 In-Reply-To: <20120417004935.a9a39d951b3c24588e29edd2@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 04/16/2012 11:49 PM, Takuya Yoshikawa wrote: > Although O(1) is actually O(1) for GET_DIRTY_LOG thread, it adds some > overheads to page fault handling. We may need to hold mmu_lock for properly > handling O(1)'s write protection and ~500 write protections will not be so > cheap. And there is no answer to the question how to achive slot-wise write > protection. > Actually no. We do not increase the overload on page fault for migration. The number of page fault of O(1) is the same as write-protect all spte. And, we can also avoid to hold mmu_lock to write-protect PML4s, we can use a generation number, and notify mmu to update its page table when dirty-log is enabled. Anyway, no performance data, no truth. Let me implement it first.