Merge branch 'for-linus' of git://git.kernel.dk/linux-2.6-block

* 'for-linus' of git://git.kernel.dk/linux-2.6-block:
  block: Range check cpu in blk_cpu_to_group
  scatterlist: prevent invalid free when alloc fails
  writeback: Fix lost wake-up shutting down writeback thread
  writeback: do not lose wakeup events when forking bdi threads
  cciss: fix reporting of max queue depth since init
  block: switch s390 tape_block and mg_disk to elevator_change()
  block: add function call to switch the IO scheduler from a driver
  fs/bio-integrity.c: return -ENOMEM on kmalloc failure
  bio-integrity.c: remove dependency on __GFP_NOFAIL
  BLOCK: fix bio.bi_rw handling
  block: put dev->kobj in blk_register_queue fail path
  cciss: handle allocation failure
  cfq-iosched: Documentation help for new tunables
  cfq-iosched: blktrace print per slice sector stats
  cfq-iosched: Implement tunable group_idle
  cfq-iosched: Do group share accounting in IOPS when slice_idle=0
  cfq-iosched: Do not idle if slice_idle=0
  cciss: disable doorbell reset on reset_devices
  blkio: Fix return code for mkdir calls

1 files changed, 28 insertions, 0 deletions

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 48e0b21b0059..6919d62591d9 100644
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -217,6 +217,7 @@ Details of cgroup files
 CFQ sysfs tunable
 =================
 /sys/block/<disk>/queue/iosched/group_isolation
+-----------------------------------------------
 
 If group_isolation=1, it provides stronger isolation between groups at the
 expense of throughput. By default group_isolation is 0. In general that
@@ -243,6 +244,33 @@ By default one should run with group_isolation=0. If that is not sufficient
 and one wants stronger isolation between groups, then set group_isolation=1
 but this will come at cost of reduced throughput.
 
+/sys/block/<disk>/queue/iosched/slice_idle
+------------------------------------------
+On a faster hardware CFQ can be slow, especially with sequential workload.
+This happens because CFQ idles on a single queue and single queue might not
+drive deeper request queue depths to keep the storage busy. In such scenarios
+one can try setting slice_idle=0 and that would switch CFQ to IOPS
+(IO operations per second) mode on NCQ supporting hardware.
+
+That means CFQ will not idle between cfq queues of a cfq group and hence be
+able to driver higher queue depth and achieve better throughput. That also
+means that cfq provides fairness among groups in terms of IOPS and not in
+terms of disk time.
+
+/sys/block/<disk>/queue/iosched/group_idle
+------------------------------------------
+If one disables idling on individual cfq queues and cfq service trees by
+setting slice_idle=0, group_idle kicks in. That means CFQ will still idle
+on the group in an attempt to provide fairness among groups.
+
+By default group_idle is same as slice_idle and does not do anything if
+slice_idle is enabled.
+
+One can experience an overall throughput drop if you have created multiple
+groups and put applications in that group which are not driving enough
+IO to keep disk busy. In that case set group_idle=0, and CFQ will not idle
+on individual groups and throughput should improve.
+
 What works
 ==========
 - Currently only sync IO queues are support. All the buffered writes are