arch/arm64/perf.rst

1 .. SPDX-License-Identifier: GPL-2.0
13 :Date: 2019-03-06
16 ------------
24 --------------
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46 For a non-VHE host this attribute will exclude EL2 as we consider the
55 ----------------------------
59 The KVM host may run at EL0 (userspace), EL1 (non-VHE kernel) and EL2 (VHE
60 kernel or non-VHE hypervisor).
65 exclusively rely on the PMU's hardware exception filtering - therefore we
67 performed differently on VHE and non-VHE systems.
69 For non-VHE systems we exclude EL2 for exclude_host - upon entering and
70 exiting the guest we disable/enable the event as appropriate based on the
75 to include/exclude EL0 as appropriate based on the exclude_host and
79 non-VHE guest however please note that EL2 is never counted within a guest.
83 --------
85 On non-VHE hosts we enable/disable counters on the entry/exit of host/guest
86 transition at EL2 - however there is a period of time between
99 --------
102 implementation is cpu-dependent.
106 This targets specifically self-monitoring tasks in order to reduce the overhead
109 How-to
110 ------
111 The focus is set on the armv8 PMUv3 which makes sure that the access to the pmu
118 .. code-block:: sh
133 and perf_evsel__read() functions. See `tools/lib/perf/tests/test-evsel.c`_ for
137 ---------------------------
143 Have a look at `tools/perf/arch/arm64/tests/user-events.c`_ for an example. It
147 .. code-block:: sh
149   perf test -v user
152 --------------------------------------
153 The user can request either a 32-bit (config1:0 == 0) or 64-bit (config1:0 == 1)
155 if a 64-bit counter is requested and the hardware doesn't support 64-bit
157 access. If a 32-bit counter is requested on hardware with 64-bit counters, then
158 userspace must treat the upper 32-bits read from the counter as UNKNOWN. The
163 .. _tools/perf/arch/arm64/tests/user-events.c:
164 …rnel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c
165 .. _tools/lib/perf/tests/test-evsel.c:
166 …//git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/perf/tests/test-evsel.c
172 --------
174 FEAT_PMUv3_TH (Armv8.8) permits a PMU counter to increment only on
185 How-to
186 ------
190 .. list-table::
191    :header-rows: 1
193    * - Parameter
194      - Description
195    * - threshold
196      - Value to threshold the event by. A value of 0 means that
198    * - threshold_compare
199      - | Comparison function to use, with the following values supported:
201        | 0: Not-equal
203        | 2: Greater-than-or-equal
204        | 3: Less-than
205    * - threshold_count
206      - If this is set, count by 1 after passing the threshold condition
212 .. code-block:: sh
214   perf stat -e stall_slot/threshold=2,threshold_compare=2/ \
215             -e dtlb_walk/threshold=10,threshold_compare=3,threshold_count/
224 .. code-block:: sh