On 16/08/2016 12:45, Punit Agrawal wrote: > Hi, > > ARMv8 supports trapping guest TLB maintenance operations to the > hypervisor. This trapping mechanism can be used to monitor the use of > guest TLB instructions. > > As taking a trap for every TLB operation can have significant > overhead, trapping should only be enabled - > > * on user request > * for the VM of interest > > This patchset adds support to listen to perf trace event state change > notifications. The notifications and associated context are then used > to enable trapping of guest TLB operations when requested by the > user. The trap handling generates trace events (kvm_tlb_invalidate) > which can already be counted using existing perf trace > functionality. > > Trapping of guest TLB operations is disabled when not being monitored > (reducing profiling overhead). > > I would appreciate feedback on the approach to tie the control of TLB > monitoring with perf trace events (Patch 1) especially if there are > any suggestions on avoiding (or reducing) the overhead of "perf trace" > notifications. > > I looked at using regfunc/unregfunc tracepoint hooks but they don't > include the event context. But the bigger problem was that the > callbacks are only called on the first instance of simultaneously > executing perf stat invocations. > > The patchset is based on v4.8-rc2 and adds support for monitoring > guest TLB operations on 64bit hosts. If the approach taken in the > patches is acceptable, I'll add 32bit host support as well. > > With this patchset, 'perf' tool when attached to a VM process can be > used to monitor the TLB operations. E.g., to monitor a VM with process > id 4166 - > > # perf stat -e "kvm:kvm_tlb_invalidate" -p 4166 > > Perform some operations in VM (running 'make -j 7' on the kernel > sources in this instance). Breaking out of perf shows - > > Performance counter stats for process id '4166': > > 7,471,974 kvm:kvm_tlb_invalidate > > 374.235405282 seconds time elapsed > > All feedback welcome. Can you explain what this is used for? In other words, why would this be used instead of just running perf in the guest? Thanks, Paolo -- 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
