From 9d87bbae2d60ebbd1f28a4b5c65162051164c775 Mon Sep 17 00:00:00 2001 From: Alexey Budankov Date: Mon, 11 Feb 2019 16:42:58 +0300 Subject: [PATCH] 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 Signed-off-by: Jonathan Corbet --- Documentation/admin-guide/perf-security.rst | 42 +++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst index f73ebfe..bac599e 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] ``_ .. [6] ``_ .. [7] ``_ +.. [11] ``_ +.. [12] ``_ -- 2.7.4