On 20/10/2015 17:26, 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.
Note that this is not a glevels _tracepoint_ field. The tracepoint field is "role" and it is a 64-bit integer. The plugin interprets the bitfields of that integer, and the position/meaning of the bitfields has changed. I guess I could use the mmu_valid_gen field as a proxy (it was introduced after glevels was removed), and only provide the "very old" (up to 2.6.34) and "new" (4.2+) formats. The "old" format (2.6.35-4.1) was never implemented in the plugin; it may well remain that way. However, it frankly seems a bit academic. The parsing _will_ work, apart from printing a nonsensical role just like it has always done for the past four years. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
