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    Subject[RFC PATCH 0/2] perf_events: add support for per-cpu per-cgroup monitoring (v3)
    This series of patches adds per-container (cgroup) filtering capability
    to per-cpu monitoring. In other words, we can monitor all threads belonging
    to a specific cgroup and running on a specific CPU.

    This is useful to measure what is going on inside a cgroup. Something that
    cannot easily and cheaply be achieved with either per-thread or per-cpu mode.
    Cgroups can span multiple CPUs. CPUs can be shared between cgroups. Cgroups
    can have lots of threads. Threads can come and go during a measurement.

    To measure per-cgroup today requires using per-thread mode and attaching to
    all the current threads inside a cgroup and tracking new threads. That would
    require scanning of /proc/PID, which is subject to race conditions, and
    creating an event for each thread, each event requiring kernel memory.

    The approach taken by this patch is to leverage the per-cpu mode by simply
    adding a filtering capability on context switch only when necessary. That
    way the amount of kernel memory used remains bound by the number of CPUs.
    We also do not have to scan /proc. We are only interested in cgroup level
    counts, not per-thread.

    The cgroup to monitor is designated by passing a file descriptor opened
    on a new per-cgroup file in the cgroup filesystem (perf_event.perf). The
    option must be activated by setting perf_event_attr.cgroup=1 and passing
    a valid file descriptor in perf_event_attr.cgroup_fd. Those are the only
    two ABI extensions.

    The patch also includes changes to the perf tool to make use of cgroup
    filtering. Both perf stat and perf record have been extended to support
    cgroup via a new -G option. The cgroup is specified per event:

    $ perf stat -B -a -e cycles:u,cycles:u,cycles:u -G test1,,test2 -- sleep 1
    Performance counter stats for 'sleep 1':

    2,368,667,414 cycles test1
    2,369,661,459 cycles
    <not counted> cycles test2

    1.001856890 seconds time elapsed

    Here, we measure cycles in 3 different cgroups. When a cgroup is omitted,
    the "root" cgroup is used, i.e., all threads executing on the monitored
    CPUs are measured.

    In the second version, time tracking has been updated. In cgroup mode,
    time_enabled tracks the time during which the cgroup was active, i.e., threads
    from the cgroup executed on the monitored CPU. The meaning of time_running
    is unchanged. In non-cgroup mode, time_enabled stills tracks wall-clock time
    for per-cpu events. Here is an example:

    In one shell I do:
    $ echo $$ >/cgroup/test1/perf_events.perf
    $ taskset -c 1 noploop 600
    In another shell I do:
    $ taskset -c 1 noploop 600

    Both noploops are competing on CPU1 (part of cgroup test1)

    $ perf stat -B -a -e cycles:u,cycles:u,cycles:u -G test1,,test2 -- sleep 1
    Performance counter stats for 'sleep 1':

    1,190,595,954 cycles test1
    2,372,471,023 cycles
    <not counted> cycles test2

    1.001845567 seconds time elapsed

    The second count reflects activity across all CPUs and cgroups.
    The first count reflects was happened inside cgroup test1. As shown,
    the noploop running inside test1, only got half the CPU time.

    In the third version, we have dropped dependency on NR_CPUS
    in favor of dynamic allocation with alloc_percpu(). We have
    also renamed get_event_time() to something more explicit:
    perf_event_time(). We cleaned the code so it compiles with
    CONFIG_CGROUPS disabled. We have also fixed a bug in the
    perf tool sampling module builtin-record.c

    PATCH 0/2: introduction
    PATCH 1/2: kernel changes
    PATCH 2/2: perf tool changes

    Signed-off-by: Stephane Eranian <>

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      Last update: 2010-09-09 15:13    [W:0.024 / U:0.528 seconds]
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