exclude_user¶

This attribute excludes userspace.

Userspace always runs at EL0 and thus this attribute will exclude EL0.

exclude_kernel¶

This attribute excludes the kernel.

The kernel runs at EL2 with VHE and EL1 without. Guest kernels always runat EL1.

For the host this attribute will exclude EL1 and additionally EL2 on a VHEsystem.

For the guest this attribute will exclude EL1. Please note that EL2 isnever counted within a guest.

exclude_hv¶

This attribute excludes the hypervisor.

For a VHE host this attribute is ignored as we consider the host kernel tobe the hypervisor.

For a non-VHE host this attribute will exclude EL2 as we consider thehypervisor to be any code that runs at EL2 which is predominantly used forguest/host transitions.

For the guest this attribute has no effect. Please note that EL2 isnever counted within a guest.

exclude_host / exclude_guest¶

These attributes exclude the KVM host and guest, respectively.

The KVM host may run at EL0 (userspace), EL1 (non-VHE kernel) and EL2 (VHEkernel or non-VHE hypervisor).

The KVM guest may run at EL0 (userspace) and EL1 (kernel).

Due to the overlapping exception levels between host and guests we cannotexclusively rely on the PMU’s hardware exception filtering - therefore wemust enable/disable counting on the entry and exit to the guest. This isperformed differently on VHE and non-VHE systems.

For non-VHE systems we exclude EL2 for exclude_host - upon entering andexiting the guest we disable/enable the event as appropriate based on theexclude_host and exclude_guest attributes.

For VHE systems we exclude EL1 for exclude_guest and exclude both EL0,EL2for exclude_host. Upon entering and exiting the guest we modify the eventto include/exclude EL0 as appropriate based on the exclude_host andexclude_guest attributes.

The statements above also apply when these attributes are used within anon-VHE guest however please note that EL2 is never counted within a guest.

Accuracy¶

On non-VHE hosts we enable/disable counters on the entry/exit of host/guesttransition at EL2 - however there is a period of time betweenenabling/disabling the counters and entering/exiting the guest. We areable to eliminate counters counting host events on the boundaries of guestentry/exit when counting guest events by filtering out EL2 forexclude_host. However when using !exclude_hv there is a small blackoutwindow at the guest entry/exit where host events are not captured.

On VHE systems there are no blackout windows.