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authorDivyesh Shah <dpshah@google.com>2010-04-08 21:15:35 -0700
committerJens Axboe <jens.axboe@oracle.com>2010-04-09 08:36:08 +0200
commit812df48d127365ffd0869aa139738f572a86759c (patch)
tree772ef559057cd432ad874cd429287e7a912b1bb3 /Documentation/cgroups
parentcdc1184cf4a7bd99f5473a91244197accc49146b (diff)
downloadlinux-linaro-android-812df48d127365ffd0869aa139738f572a86759c.tar.gz
blkio: Add more debug-only per-cgroup stats
1) group_wait_time - This is the amount of time the cgroup had to wait to get a timeslice for one of its queues from when it became busy, i.e., went from 0 to 1 request queued. This is different from the io_wait_time which is the cumulative total of the amount of time spent by each IO in that cgroup waiting in the scheduler queue. This stat is a great way to find out any jobs in the fleet that are being starved or waiting for longer than what is expected (due to an IO controller bug or any other issue). 2) empty_time - This is the amount of time a cgroup spends w/o any pending requests. This stat is useful when a job does not seem to be able to use its assigned disk share by helping check if that is happening due to an IO controller bug or because the job is not submitting enough IOs. 3) idle_time - This is the amount of time spent by the IO scheduler idling for a given cgroup in anticipation of a better request than the exising ones from other queues/cgroups. All these stats are recorded using start and stop events. When reading these stats, we do not add the delta between the current time and the last start time if we're between the start and stop events. We avoid doing this to make sure that these numbers are always monotonically increasing when read. Since we're using sched_clock() which may use the tsc as its source, it may induce some inconsistency (due to tsc resync across cpus) if we included the current delta. Signed-off-by: Divyesh Shah<dpshah@google.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'Documentation/cgroups')
-rw-r--r--Documentation/cgroups/blkio-controller.txt29
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 6e52e7c512a..db054ea3e7f 100644
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -150,6 +150,35 @@ Details of cgroup files
cgroup's existence. Queue size samples are taken each time one of the
queues of this cgroup gets a timeslice.
+- blkio.group_wait_time
+ - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+ This is the amount of time the cgroup had to wait since it became busy
+ (i.e., went from 0 to 1 request queued) to get a timeslice for one of
+ its queues. This is different from the io_wait_time which is the
+ cumulative total of the amount of time spent by each IO in that cgroup
+ waiting in the scheduler queue. This is in nanoseconds. If this is
+ read when the cgroup is in a waiting (for timeslice) state, the stat
+ will only report the group_wait_time accumulated till the last time it
+ got a timeslice and will not include the current delta.
+
+- blkio.empty_time
+ - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+ This is the amount of time a cgroup spends without any pending
+ requests when not being served, i.e., it does not include any time
+ spent idling for one of the queues of the cgroup. This is in
+ nanoseconds. If this is read when the cgroup is in an empty state,
+ the stat will only report the empty_time accumulated till the last
+ time it had a pending request and will not include the current delta.
+
+- blkio.idle_time
+ - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+ This is the amount of time spent by the IO scheduler idling for a
+ given cgroup in anticipation of a better request than the exising ones
+ from other queues/cgroups. This is in nanoseconds. If this is read
+ when the cgroup is in an idling state, the stat will only report the
+ idle_time accumulated till the last idle period and will not include
+ the current delta.
+
- blkio.dequeue
- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This
gives the statistics about how many a times a group was dequeued