Messages in this thread | | | Date | Sun, 10 Feb 2019 23:34:21 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v2 1/4] perf-security: document perf_events/Perf resource control |
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On Thu, 7 Feb 2019, Alexey Budankov wrote:
General note: Please stay in the 80 char limit for all of the text.
> +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.
I'd move this sentence into a different paragraph and keep those related to RLIMIT_NOFILE together.
> ... RLIMIT_NOFILE limit can be increased on per-user basis modifying > +content of the limits.conf file [12]_ on some systems.
On some systems?
> Ordinarily, a Perf sampling session > +(perf record) requires an amount of open perf_event file descriptors that is not > +less than a number of monitored events multiplied by a number of monitored CPUs.
s/a number of/the number of/
The ordinary use case is:
perf CMD pile-of-events PROCESS
which does not specify the monitored CPUs at all. Then the number of file descriptors is NR_EVENTS * NR_ONLINE_CPUS.
> +An amount of memory available to user processes for capturing performance monitoring
The amount ...
> +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 specially
s/specially/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 available 4128 KiB between the
distribute the available
> +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 costraints are ignored for
constraints.
> +processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users
what means perf_events/Perf ?
> +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.
Thanks,
tglx
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