diff options
Diffstat (limited to 'Documentation/arm64')
| -rw-r--r-- | Documentation/arm64/cpu-feature-registers.rst | 17 | ||||
| -rw-r--r-- | Documentation/arm64/elf_hwcaps.rst | 8 | ||||
| -rw-r--r-- | Documentation/arm64/perf.rst | 78 | ||||
| -rw-r--r-- | Documentation/arm64/sve.rst | 2 | ||||
| -rw-r--r-- | Documentation/arm64/tagged-address-abi.rst | 2 |
5 files changed, 104 insertions, 3 deletions
diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst index 9f9b8fd06089..749ae970c319 100644 --- a/Documentation/arm64/cpu-feature-registers.rst +++ b/Documentation/arm64/cpu-feature-registers.rst @@ -275,6 +275,23 @@ infrastructure: | SVEVer | [3-0] | y | +------------------------------+---------+---------+ + 8) ID_AA64MMFR1_EL1 - Memory model feature register 1 + + +------------------------------+---------+---------+ + | Name | bits | visible | + +------------------------------+---------+---------+ + | AFP | [47-44] | y | + +------------------------------+---------+---------+ + + 9) ID_AA64ISAR2_EL1 - Instruction set attribute register 2 + + +------------------------------+---------+---------+ + | Name | bits | visible | + +------------------------------+---------+---------+ + | RPRES | [7-4] | y | + +------------------------------+---------+---------+ + + Appendix I: Example ------------------- diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst index af106af8e1c0..b72ff17d600a 100644 --- a/Documentation/arm64/elf_hwcaps.rst +++ b/Documentation/arm64/elf_hwcaps.rst @@ -251,6 +251,14 @@ HWCAP2_ECV Functionality implied by ID_AA64MMFR0_EL1.ECV == 0b0001. +HWCAP2_AFP + + Functionality implied by ID_AA64MFR1_EL1.AFP == 0b0001. + +HWCAP2_RPRES + + Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001. + 4. Unused AT_HWCAP bits ----------------------- diff --git a/Documentation/arm64/perf.rst b/Documentation/arm64/perf.rst index b567f177d385..1f87b57c2332 100644 --- a/Documentation/arm64/perf.rst +++ b/Documentation/arm64/perf.rst @@ -2,7 +2,10 @@ .. _perf_index: -===================== +==== +Perf +==== + Perf Event Attributes ===================== @@ -88,3 +91,76 @@ 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 diff --git a/Documentation/arm64/sve.rst b/Documentation/arm64/sve.rst index 03137154299e..9d9a4de5bc34 100644 --- a/Documentation/arm64/sve.rst +++ b/Documentation/arm64/sve.rst @@ -255,7 +255,7 @@ prctl(PR_SVE_GET_VL) vector length change (which would only normally be the case between a fork() or vfork() and the corresponding execve() in typical use). - To extract the vector length from the result, and it with + To extract the vector length from the result, bitwise and it with PR_SVE_VL_LEN_MASK. Return value: a nonnegative value on success, or a negative value on error: diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst index 0c9120ec58ae..540a1d4fc6c9 100644 --- a/Documentation/arm64/tagged-address-abi.rst +++ b/Documentation/arm64/tagged-address-abi.rst @@ -49,7 +49,7 @@ how the user addresses are used by the kernel: - ``brk()``, ``mmap()`` and the ``new_address`` argument to ``mremap()`` as these have the potential to alias with existing - user addresses. + user addresses. NOTE: This behaviour changed in v5.6 and so some earlier kernels may incorrectly accept valid tagged pointers for the ``brk()``, |