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author | 2019-02-11 16:42:58 +0300 | |
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committer | 2019-02-17 16:04:45 -0700 | |
commit | 9d87bbae2d60ebbd1f28a4b5c65162051164c775 (patch) | |
tree | 29bcf1fad4b018ac7fe0580b4862c2392bb7b124 /Documentation/admin-guide/perf-security.rst | |
parent | sysfs.txt: add note on available attribute macros (diff) | |
download | linux-9d87bbae2d60ebbd1f28a4b5c65162051164c775.tar.gz linux-9d87bbae2d60ebbd1f28a4b5c65162051164c775.tar.bz2 linux-9d87bbae2d60ebbd1f28a4b5c65162051164c775.zip |
perf-security: document perf_events/Perf resource control
Extend perf-security.rst file with perf_events/Perf resource control
section describing RLIMIT_NOFILE and perf_event_mlock_kb settings for
performance monitoring user processes.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/admin-guide/perf-security.rst')
-rw-r--r-- | Documentation/admin-guide/perf-security.rst | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst index f73ebfe9bfe2..bac599e3c55f 100644 --- a/Documentation/admin-guide/perf-security.rst +++ b/Documentation/admin-guide/perf-security.rst @@ -84,6 +84,46 @@ governed by perf_event_paranoid [2]_ setting: locking limit is imposed but ignored for unprivileged processes with CAP_IPC_LOCK capability. +perf_events/Perf resource control +--------------------------------- + +Open file descriptors ++++++++++++++++++++++ + +The perf_events system call API [2]_ allocates file descriptors for every configured +PMU event. Open file descriptors are a per-process accountable resource governed +by the RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login +shell process. When configuring Perf collection for a long list of events on a +large server system, this limit can be easily hit preventing required monitoring +configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying +content of the limits.conf file [12]_ . Ordinarily, a Perf sampling session +(perf record) requires an amount of open perf_event file descriptors that is not +less than the number of monitored events multiplied by the number of monitored CPUs. + +Memory allocation ++++++++++++++++++ + +The amount of memory available to user processes for capturing performance monitoring +data is governed by the perf_event_mlock_kb [2]_ setting. This perf_event specific +resource setting defines overall per-cpu limits of memory allowed for mapping +by the user processes to execute performance monitoring. The setting essentially +extends the RLIMIT_MEMLOCK [11]_ limit, but only for memory regions mapped specifically +for capturing monitored performance events and related data. + +For example, if a machine has eight cores and perf_event_mlock_kb limit is set +to 516 KiB, then a user process is provided with 516 KiB * 8 = 4128 KiB of memory +above the RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular, +this means that, if the user wants to start two or more performance monitoring +processes, the user is required to manually distribute the available 4128 KiB between the +monitoring processes, for example, using the --mmap-pages Perf record mode option. +Otherwise, the first started performance monitoring process allocates all available +4128 KiB and the other processes will fail to proceed due to the lack of memory. + +RLIMIT_MEMLOCK and perf_event_mlock_kb resource constraints are ignored for +processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users +can be provided with memory above the constraints for perf_events/Perf performance +monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability. + Bibliography ------------ @@ -94,4 +134,6 @@ Bibliography .. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_ .. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_ .. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_ +.. [11] `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_ +.. [12] `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_ |