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diff --git a/Documentation/arm64/perf.rst b/Documentation/arm64/perf.rst deleted file mode 100644 index 1f87b57c2332..000000000000 --- a/Documentation/arm64/perf.rst +++ /dev/null @@ -1,166 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -.. _perf_index: - -==== -Perf -==== - -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. - -Perf Userspace PMU Hardware Counter Access -========================================== - -Overview --------- -The perf userspace tool relies on the PMU to monitor events. It offers an -abstraction layer over the hardware counters since the underlying -implementation is cpu-dependent. -Arm64 allows userspace tools to have access to the registers storing the -hardware counters' values directly. - -This targets specifically self-monitoring tasks in order to reduce the overhead -by directly accessing the registers without having to go through the kernel. - -How-to ------- -The focus is set on the armv8 PMUv3 which makes sure that the access to the pmu -registers is enabled and that the userspace has access to the relevant -information in order to use them. - -In order to have access to the hardware counters, the global sysctl -kernel/perf_user_access must first be enabled: - -.. code-block:: sh - - echo 1 > /proc/sys/kernel/perf_user_access - -It is necessary to open the event using the perf tool interface with config1:1 -attr bit set: the sys_perf_event_open syscall returns a fd which can -subsequently be used with the mmap syscall in order to retrieve a page of memory -containing information about the event. The PMU driver uses this page to expose -to the user the hardware counter's index and other necessary data. Using this -index enables the user to access the PMU registers using the `mrs` instruction. -Access to the PMU registers is only valid while the sequence lock is unchanged. -In particular, the PMSELR_EL0 register is zeroed each time the sequence lock is -changed. - -The userspace access is supported in libperf using the perf_evsel__mmap() -and perf_evsel__read() functions. See `tools/lib/perf/tests/test-evsel.c`_ for -an example. - -About heterogeneous systems ---------------------------- -On heterogeneous systems such as big.LITTLE, userspace PMU counter access can -only be enabled when the tasks are pinned to a homogeneous subset of cores and -the corresponding PMU instance is opened by specifying the 'type' attribute. -The use of generic event types is not supported in this case. - -Have a look at `tools/perf/arch/arm64/tests/user-events.c`_ for an example. It -can be run using the perf tool to check that the access to the registers works -correctly from userspace: - -.. code-block:: sh - - perf test -v user - -About chained events and counter sizes --------------------------------------- -The user can request either a 32-bit (config1:0 == 0) or 64-bit (config1:0 == 1) -counter along with userspace access. The sys_perf_event_open syscall will fail -if a 64-bit counter is requested and the hardware doesn't support 64-bit -counters. Chained events are not supported in conjunction with userspace counter -access. If a 32-bit counter is requested on hardware with 64-bit counters, then -userspace must treat the upper 32-bits read from the counter as UNKNOWN. The -'pmc_width' field in the user page will indicate the valid width of the counter -and should be used to mask the upper bits as needed. - -.. Links -.. _tools/perf/arch/arm64/tests/user-events.c: - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c -.. _tools/lib/perf/tests/test-evsel.c: - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/perf/tests/test-evsel.c |