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-rw-r--r--Documentation/cgroups/blkio-controller.txt28
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
217CFQ sysfs tunable 217CFQ sysfs tunable
218================= 218=================
219/sys/block/<disk>/queue/iosched/group_isolation 219/sys/block/<disk>/queue/iosched/group_isolation
220-----------------------------------------------
220 221
221If group_isolation=1, it provides stronger isolation between groups at the 222If group_isolation=1, it provides stronger isolation between groups at the
222expense of throughput. By default group_isolation is 0. In general that 223expense 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
243and one wants stronger isolation between groups, then set group_isolation=1 244and one wants stronger isolation between groups, then set group_isolation=1
244but this will come at cost of reduced throughput. 245but this will come at cost of reduced throughput.
245 246
247/sys/block/<disk>/queue/iosched/slice_idle
248------------------------------------------
249On a faster hardware CFQ can be slow, especially with sequential workload.
250This happens because CFQ idles on a single queue and single queue might not
251drive deeper request queue depths to keep the storage busy. In such scenarios
252one can try setting slice_idle=0 and that would switch CFQ to IOPS
253(IO operations per second) mode on NCQ supporting hardware.
254
255That means CFQ will not idle between cfq queues of a cfq group and hence be
256able to driver higher queue depth and achieve better throughput. That also
257means that cfq provides fairness among groups in terms of IOPS and not in
258terms of disk time.
259
260/sys/block/<disk>/queue/iosched/group_idle
261------------------------------------------
262If one disables idling on individual cfq queues and cfq service trees by
263setting slice_idle=0, group_idle kicks in. That means CFQ will still idle
264on the group in an attempt to provide fairness among groups.
265
266By default group_idle is same as slice_idle and does not do anything if
267slice_idle is enabled.
268
269One can experience an overall throughput drop if you have created multiple
270groups and put applications in that group which are not driving enough
271IO to keep disk busy. In that case set group_idle=0, and CFQ will not idle
272on individual groups and throughput should improve.
273
246What works 274What works
247========== 275==========
248- Currently only sync IO queues are support. All the buffered writes are 276- Currently only sync IO queues are support. All the buffered writes are