| Andrew Murray | a9bf313 | 2019-04-09 20:22:17 +0100 | [diff] [blame^] | 1 | Perf Event Attributes |
| 2 | ===================== |
| 3 | |
| 4 | Author: Andrew Murray <andrew.murray@arm.com> |
| 5 | Date: 2019-03-06 |
| 6 | |
| 7 | exclude_user |
| 8 | ------------ |
| 9 | |
| 10 | This attribute excludes userspace. |
| 11 | |
| 12 | Userspace always runs at EL0 and thus this attribute will exclude EL0. |
| 13 | |
| 14 | |
| 15 | exclude_kernel |
| 16 | -------------- |
| 17 | |
| 18 | This attribute excludes the kernel. |
| 19 | |
| 20 | The kernel runs at EL2 with VHE and EL1 without. Guest kernels always run |
| 21 | at EL1. |
| 22 | |
| 23 | For the host this attribute will exclude EL1 and additionally EL2 on a VHE |
| 24 | system. |
| 25 | |
| 26 | For the guest this attribute will exclude EL1. Please note that EL2 is |
| 27 | never counted within a guest. |
| 28 | |
| 29 | |
| 30 | exclude_hv |
| 31 | ---------- |
| 32 | |
| 33 | This attribute excludes the hypervisor. |
| 34 | |
| 35 | For a VHE host this attribute is ignored as we consider the host kernel to |
| 36 | be the hypervisor. |
| 37 | |
| 38 | For a non-VHE host this attribute will exclude EL2 as we consider the |
| 39 | hypervisor to be any code that runs at EL2 which is predominantly used for |
| 40 | guest/host transitions. |
| 41 | |
| 42 | For the guest this attribute has no effect. Please note that EL2 is |
| 43 | never counted within a guest. |
| 44 | |
| 45 | |
| 46 | exclude_host / exclude_guest |
| 47 | ---------------------------- |
| 48 | |
| 49 | These attributes exclude the KVM host and guest, respectively. |
| 50 | |
| 51 | The KVM host may run at EL0 (userspace), EL1 (non-VHE kernel) and EL2 (VHE |
| 52 | kernel or non-VHE hypervisor). |
| 53 | |
| 54 | The KVM guest may run at EL0 (userspace) and EL1 (kernel). |
| 55 | |
| 56 | Due to the overlapping exception levels between host and guests we cannot |
| 57 | exclusively rely on the PMU's hardware exception filtering - therefore we |
| 58 | must enable/disable counting on the entry and exit to the guest. This is |
| 59 | performed differently on VHE and non-VHE systems. |
| 60 | |
| 61 | For non-VHE systems we exclude EL2 for exclude_host - upon entering and |
| 62 | exiting the guest we disable/enable the event as appropriate based on the |
| 63 | exclude_host and exclude_guest attributes. |
| 64 | |
| 65 | For VHE systems we exclude EL1 for exclude_guest and exclude both EL0,EL2 |
| 66 | for exclude_host. Upon entering and exiting the guest we modify the event |
| 67 | to include/exclude EL0 as appropriate based on the exclude_host and |
| 68 | exclude_guest attributes. |
| 69 | |
| 70 | The statements above also apply when these attributes are used within a |
| 71 | non-VHE guest however please note that EL2 is never counted within a guest. |
| 72 | |
| 73 | |
| 74 | Accuracy |
| 75 | -------- |
| 76 | |
| 77 | On non-VHE hosts we enable/disable counters on the entry/exit of host/guest |
| 78 | transition at EL2 - however there is a period of time between |
| 79 | enabling/disabling the counters and entering/exiting the guest. We are |
| 80 | able to eliminate counters counting host events on the boundaries of guest |
| 81 | entry/exit when counting guest events by filtering out EL2 for |
| 82 | exclude_host. However when using !exclude_hv there is a small blackout |
| 83 | window at the guest entry/exit where host events are not captured. |
| 84 | |
| 85 | On VHE systems there are no blackout windows. |