Messages in this thread | | | From | Stephane Eranian <> | Date | Mon, 14 Feb 2011 11:20:01 +0200 | Subject | [PATCH 0/2] perf_events: add support for per-cpu per-cgroup monitoring (v9) |
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[depends on cgroup patch set: cgroup: Fix cgroup_subsys::exit callback]
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, samples and not thread level.
The cgroup to monitor is designated by passing a file descriptor opened on the cgroup directory name in the cgroup filesystem. The cgroup mode is activated by passing a flag value in the perf_event syscall.
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 still 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 what happened inside cgroup test1. As shown, the noploop running inside test1, only got half the CPU cycles.
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
In this fourth version, we have dropped changes to perf_event_attr. Instead we pass the cgroup file descriptor in the pid argument to the syscall and we active cgroup mode by passing PERF_FLAG_PID_CGROUP into flags.
The fifth version updates the patch to 2.6.37-rc2 and contains improved time tracking support. Several bug fixes and cleanups. Context switch impact is also mitigated with dynamic jump labels.
The sixth version breaks the series of patches into 5 parts and also updates the patch to 2.6.37-rc4-tip. It also includes a few bug fixes.
In the seventh version, we upate the patch to 2.6.37-rc8-tip, and cleanup the code some more based on LKML comments. This patch adds a CONFIG_CGROUP_PERF option dependent on PERF_EVENTS && CGROUPS.
In the eighth version, we have fixed some important issues related to cgroup switches and the way we handle exiting tasks (do_exit()). We have also updated the perf tool patch to support a variable number of events (and thus cgroups).
In the ninth version, Peter Zijlstra removed the hack in cgroup_exit() and used the ss->attach() callback instead. Note however, that the perf cgroup patch now depends on a cgroup patch by Peter. This version also simplifies event_filter_match() because the current active cgrp is stored in cpuctx now (patch by Peter). The patch series also updates the perf tool cgroup support to the latest version incl. support for evsel. Thanks to Peter for his help with this patchset.
PATCH 0/2: introduction PATCH 1/2: actual cgroup support PATCH 2/2: perf tool changes for cgroup
Signed-off-by: Stephane Eranian <eranian@google.com>
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