On Tue, 20 Oct 2015 17:19:12 +0200 Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > 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. Can we add a check if glevels field exists, and do the old format if it does? I'm very strict on making sure event-parse works with all incarnations of kernels. > > 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. Thanks for the update. -- Steve -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
