docs: arm64: convert perf.txt to ReST format

This file is almost in ReST. All it needs is a rename and
adding a :field: for the two fields at the beginning
(author and date).

While here, add a proper SPDX header, and use the standard
markup for document titles, just for consistency.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/c99bebf166559e9098a9eb78fb2eab2847fffb05.1592203650.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 88 insertions, 0 deletions

diff --git a/Documentation/arm64/perf.rst b/Documentation/arm64/perf.rst
new file mode 100644
index 000000000000..9c76a97baf28
--- /dev/null
+++ b/Documentation/arm64/perf.rst
@@ -0,0 +1,88 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Perf Event Attributes
+=====================
+
+:Author: Andrew Murray <andrew.murray@arm.com>
+:Date: 2019-03-06
+
+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 run
+at EL1.
+
+For the host this attribute will exclude EL1 and additionally EL2 on a VHE
+system.
+
+For the guest this attribute will exclude EL1. Please note that EL2 is
+never 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 to
+be the hypervisor.
+
+For a non-VHE host this attribute will exclude EL2 as we consider the
+hypervisor to be any code that runs at EL2 which is predominantly used for
+guest/host transitions.
+
+For the guest this attribute has no effect. Please note that EL2 is
+never 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 (VHE
+kernel 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 cannot
+exclusively rely on the PMU's hardware exception filtering - therefore we
+must enable/disable counting on the entry and exit to the guest. This is
+performed differently on VHE and non-VHE systems.
+
+For non-VHE systems we exclude EL2 for exclude_host - upon entering and
+exiting the guest we disable/enable the event as appropriate based on the
+exclude_host and exclude_guest attributes.
+
+For VHE systems we exclude EL1 for exclude_guest and exclude both EL0,EL2
+for exclude_host. Upon entering and exiting the guest we modify the event
+to include/exclude EL0 as appropriate based on the exclude_host and
+exclude_guest attributes.
+
+The statements above also apply when these attributes are used within a
+non-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/guest
+transition at EL2 - however there is a period of time between
+enabling/disabling the counters and entering/exiting the guest. We are
+able to eliminate counters counting host events on the boundaries of guest
+entry/exit when counting guest events by filtering out EL2 for
+exclude_host. However when using !exclude_hv there is a small blackout
+window at the guest entry/exit where host events are not captured.
+
+On VHE systems there are no blackout windows.