blkio: Add more debug-only per-cgroup stats

[safe/jmp/linux-2.6] / Documentation / cgroups / blkio-controller.txt

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 6e52e7c..db054ea 100644 (file)
--- 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