[ +PeterZ who should've been cc'd but doesn't show up in get_maintainers ] Punit Agrawal <punit.agrawal@xxxxxxx> writes: > Hi, > > This is the fourth posting of this series. The biggest change compared > to previous vesion is the addition of support for ARM hosts. With the > addition of ARM support, the patchset is now more complete. Prior > versions can be found at [0][1][2]. > > I would particularly appreciate feedback from maintainers on the > approach to tie the control of TLB monitoring with perf trace events > (Patch 3 and 4) 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. I had a chance to discuss this patchset with SteveR and PeterZ at LPC and both don't like the idea of introducing notifications on perf trace event [un]registration. Peter suggested using the PMU interface to expose this functionality. As we want to monitor TLB instructions for for each VM, this will require creating a PMU per-VM. The PMU events can be extended in the future if monitoring of additional operations is supported and required. I'll post the next version with the above changes - please chime-in if you disagrees with this approach. Thanks, Punit > > Changelog and previous cover-letter follows. > > Changes: > > v1 -> v2 > > * New (Patch 6) - Add support for trapping and emulating TLB > operations to ARM hosts > * Move common code to handle perf trace notifications to virt/kvm/arm > * Move tracepoint to include/trace/events/kvm.h > * Drop patch to introduce __tlbi helper as it is now merged > * Reorder patches > > RFC v2 -> v1 > * Dropped the RFC tag > * Patch 2 - Use VM thread group id for identification > * Patch 4 - Update comment for clarity > * Patch 6 - Add comment explaining switch to hype-role when VHE is enabled > * Patch 7 - Add comment to clarify struct kvm_trace_hook > > RFC -> RFC v2 > * Patch 4 - Rename left-over TLBI macro to __TLBI > * Patch 6 - Replace individual TLB operation emulation with > invalidating all stage 1 TLB for the VM. TLB monitoring is expected > to be a debug feature and performance is not critical. > > Although there are no PMU events to monitor TLB operations, 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. > > 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 > > Thanks, > Punit > > [0] http://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1210715.html > [1] http://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1224353.html > [2] https://marc.info/?l=linux-kernel&m=147376184208258&w=2 > > Mark Rutland (1): > arm64/kvm: hyp: tlb: use __tlbi() helper > > Punit Agrawal (7): > KVM: Track the pid of the VM process > perf/trace: Add notification for perf trace events > KVM: arm/arm64: Register perf trace event notifier > KVM: Add event to trace tlb invalidations > arm: KVM: Handle trappable TLB instructions > arm64: KVM: Handle trappable TLB instructions > KVM: arm/arm64: Enable selective trapping of TLB instructions > > arch/arm/include/asm/kvm_asm.h | 1 + > arch/arm/include/asm/kvm_host.h | 8 ++ > arch/arm/kvm/Kconfig | 4 + > arch/arm/kvm/Makefile | 1 + > arch/arm/kvm/arm.c | 2 + > arch/arm/kvm/coproc.c | 55 ++++++++++++++ > arch/arm/kvm/hyp/tlb.c | 33 ++++++++ > arch/arm64/include/asm/kvm_asm.h | 1 + > arch/arm64/include/asm/kvm_host.h | 8 ++ > arch/arm64/kvm/Kconfig | 4 + > arch/arm64/kvm/Makefile | 1 + > arch/arm64/kvm/hyp/tlb.c | 87 +++++++++++++++++++-- > arch/arm64/kvm/sys_regs.c | 81 ++++++++++++++++++++ > include/linux/kvm_host.h | 1 + > include/linux/trace_events.h | 3 + > include/trace/events/kvm.h | 17 +++++ > kernel/trace/trace_event_perf.c | 24 ++++++ > virt/kvm/arm/perf_trace.c | 154 ++++++++++++++++++++++++++++++++++++++ > virt/kvm/kvm_main.c | 2 + > 19 files changed, 481 insertions(+), 6 deletions(-) > create mode 100644 virt/kvm/arm/perf_trace.c -- 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
