linux/include
Stephane Eranian e050e3f0a7 perf: Fix broken interrupt rate throttling
This patch fixes the sampling interrupt throttling mechanism.

It was broken in v3.2. Events were not being unthrottled. The
unthrottling mechanism required that events be checked at each
timer tick.

This patch solves this problem and also separates:

  - unthrottling
  - multiplexing
  - frequency-mode period adjustments

Not all of them need to be executed at each timer tick.

This third version of the patch is based on my original patch +
PeterZ proposal (https://lkml.org/lkml/2012/1/7/87).

At each timer tick, for each context:

  - if the current CPU has throttled events, we unthrottle events

  - if context has frequency-based events, we adjust sampling periods

  - if we have reached the jiffies interval, we multiplex (rotate)

We decoupled rotation (multiplexing) from frequency-mode sampling
period adjustments.  They should not necessarily happen at the same
rate. Multiplexing is subject to jiffies_interval (currently at 1
but could be higher once the tunable is exposed via sysfs).

We have grouped frequency-mode adjustment and unthrottling into the
same routine to minimize code duplication. When throttled while in
frequency mode, we scan the events only once.

We have fixed the threshold enforcement code in __perf_event_overflow().
There was a bug whereby it would allow more than the authorized rate
because an increment of hwc->interrupts was not executed at the right
place.

The patch was tested with low sampling limit (2000) and fixed periods,
frequency mode, overcommitted PMU.

On a 2.1GHz AMD CPU:

 $ cat /proc/sys/kernel/perf_event_max_sample_rate
 2000

We set a rate of 3000 samples/sec (2.1GHz/3000 = 700000):

 $ perf record -e cycles,cycles -c 700000  noploop 10
 $ perf report -D | tail -21

 Aggregated stats:
           TOTAL events:      80086
            MMAP events:         88
            COMM events:          2
            EXIT events:          4
        THROTTLE events:      19996
      UNTHROTTLE events:      19996
          SAMPLE events:      40000

 cycles stats:
           TOTAL events:      40006
            MMAP events:          5
            COMM events:          1
            EXIT events:          4
        THROTTLE events:       9998
      UNTHROTTLE events:       9998
          SAMPLE events:      20000

 cycles stats:
           TOTAL events:      39996
        THROTTLE events:       9998
      UNTHROTTLE events:       9998
          SAMPLE events:      20000

For 10s, the cap is 2x2000x10 = 40000 samples.
We get exactly that: 20000 samples/event.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: <stable@kernel.org> # v3.2+
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120126160319.GA5655@quad
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2012-01-27 12:06:39 +01:00
..
acpi Merge branches 'atomicio-apei', 'hotplug', 'sony-nvs-nosave' and 'thermal-netlink' into release 2012-01-23 19:47:06 -05:00
asm-generic Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
crypto crypto: serpent-sse2 - add lrw support 2011-11-21 16:13:24 +08:00
drm drm: Fix authentication kernel crash 2012-01-25 09:27:45 +00:00
keys keys: add a "logon" key type 2012-01-17 22:39:40 -06:00
linux perf: Fix broken interrupt rate throttling 2012-01-27 12:06:39 +01:00
math-emu
media Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media 2012-01-18 12:53:54 -08:00
misc
mtd mtd: document that MEMWRITE ioctl is NAND-specific 2012-01-09 18:18:36 +00:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2012-01-24 15:51:40 -08:00
pcmcia
rdma rdma/core: Fix sparse warnings 2012-01-04 09:17:45 -08:00
rxrpc
scsi [SCSI] libfc: Declare local functions static 2012-01-16 12:45:48 +04:00
sound Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound 2012-01-12 08:00:30 -08:00
target target: Set additional sense length field in sense data 2011-12-16 06:29:04 +00:00
trace Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs 2012-01-17 15:49:54 -08:00
video Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
xen Merge branch 'for-3.3/drivers' of git://git.kernel.dk/linux-block 2012-01-15 12:48:41 -08:00
Kbuild