From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] tools lib traceevent: update KVM plugin Date: Tue, 20 Oct 2015 17:19:12 +0200 Message-ID: <56265B70.1000206@redhat.com> References: <1443695293-31127-1-git-send-email-pbonzini@redhat.com> <56181F25.2070402@redhat.com> <20151020143244.GG4400@redhat.com> <20151020104459.7e7f7e77@gandalf.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, acme@kernel.org To: Steven Rostedt , Arnaldo Carvalho de Melo Return-path: In-Reply-To: <20151020104459.7e7f7e77@gandalf.local.home> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 20/10/2015 16:44, Steven Rostedt wrote: > What happens if you run new perf on an older kernel. Is this new plugin > going to be screwed up? Plugins should be backward compatible. If you run new perf on older kernel, the new plugin will print the "role" field (see kvm_mmu_print_role) slightly incorrectly. That said, the existing plugin was _also_ printing the role in a wildly wrong format, like 2.6.35 vintage; the glevels field was removed by commit 5b7e0102ae74, "KVM: MMU: Replace role.glevels with role.cr4_pae", in April 2010. Going forward it's really unlikely that the role will change apart from adding new bits. These can be added to the plugin while keeping it backwards-compatible. Addition to the role happen when you implement new virtual MMU features such as SMEP, SMAP or SMM. That's once per year or less. > Is the plugin even still needed? I'm looking at some of the kvm events > and they seem to be mostly self sufficient. What ones need a plugin > today? Yes, most of them are. It's only needed for kvm_mmu_get_page, kvm_mmu_prepare_zap_page and kvm_emulate_insn. The latter is only interesting if you install the disassembler library, and I wouldn't really care if it went away. kvm_mmu_get_page and kvm_mmu_prepare_zap_page, however, have output like kvm_mmu_get_page: [FAILED TO PARSE] mmu_valid_gen=0x2 gfn=786432 role=1923 root_count=0 unsync=0 created=1 without the plugin vs. kvm_mmu_get_page: new sp gfn c0000 3 q0 direct rwx !pae !nxe !wp root 0 sync with the plugin. Paolo