From 86de78d2c5f45481945232c7d4a051aedb1f73a0 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Mon, 15 Jun 2020 08:50:19 +0200 Subject: 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 Link: https://lore.kernel.org/r/c99bebf166559e9098a9eb78fb2eab2847fffb05.1592203650.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet --- Documentation/arm64/perf.rst | 88 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 Documentation/arm64/perf.rst (limited to 'Documentation/arm64/perf.rst') 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 +: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. -- cgit