Documentation/arm64/perf.rst

1 .. SPDX-License-Identifier: GPL-2.0
8 :Date: 2019-03-06
11 ------------
15 Userspace always runs at EL0 and thus this attribute will exclude EL0.
19 --------------
23 The kernel runs at EL2 with VHE and EL1 without. Guest kernels always run
26 For the host this attribute will exclude EL1 and additionally EL2 on a VHE
34 ----------
41 For a non-VHE host this attribute will exclude EL2 as we consider the
42 hypervisor to be any code that runs at EL2 which is predominantly used for
50 ----------------------------
54 The KVM host may run at EL0 (userspace), EL1 (non-VHE kernel) and EL2 (VHE
55 kernel or non-VHE hypervisor).
60 exclusively rely on the PMU's hardware exception filtering - therefore we
61 must enable/disable counting on the entry and exit to the guest. This is
62 performed differently on VHE and non-VHE systems.
64 For non-VHE systems we exclude EL2 for exclude_host - upon entering and
65 exiting the guest we disable/enable the event as appropriate based on the
70 to include/exclude EL0 as appropriate based on the exclude_host and
74 non-VHE guest however please note that EL2 is never counted within a guest.
78 --------
80 On non-VHE hosts we enable/disable counters on the entry/exit of host/guest
81 transition at EL2 - however there is a period of time between
83 able to eliminate counters counting host events on the boundaries of guest
88 On VHE systems there are no blackout windows.