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authorJustin TerAvest <teravest@google.com>2011-03-01 15:05:08 -0500
committerJens Axboe <jaxboe@fusionio.com>2011-03-01 15:05:08 -0500
commit0bbfeb8320421989d3e12bd95fae86b9ac0712aa (patch)
treea23bb6686bd2586fe7c27d0773c63f9aeb254cd1 /Documentation
parent6fae9c25134baffbeeb20031479e7ff6f6d8eec0 (diff)
cfq-iosched: Always provide group isolation.
Effectively, make group_isolation=1 the default and remove the tunable. The setting group_isolation=0 was because by default we idle on sync-noidle tree and on fast devices, this can be very harmful for throughput. However, this problem can also be addressed by tuning slice_idle and possibly group_idle on faster storage devices. This change simplifies the CFQ code by removing the feature entirely. Signed-off-by: Justin TerAvest <teravest@google.com> Acked-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/cgroups/blkio-controller.txt28
1 files changed, 0 insertions, 28 deletions
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 4ed7b5ceeed2..d915c16df42c 100644
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -343,34 +343,6 @@ Common files among various policies
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
-means that if group_isolation=0, expect fairness for sequential workload
-only. Set group_isolation=1 to see fairness for random IO workload also.
-
-Generally CFQ will put random seeky workload in sync-noidle category. CFQ
-will disable idling on these queues and it does a collective idling on group
-of such queues. Generally these are slow moving queues and if there is a
-sync-noidle service tree in each group, that group gets exclusive access to
-disk for certain period. That means it will bring the throughput down if
-group does not have enough IO to drive deeper queue depths and utilize disk
-capacity to the fullest in the slice allocated to it. But the flip side is
-that even a random reader should get better latencies and overall throughput
-if there are lots of sequential readers/sync-idle workload running in the
-system.
-
-If group_isolation=0, then CFQ automatically moves all the random seeky queues
-in the root group. That means there will be no service differentiation for
-that kind of workload. This leads to better throughput as we do collective
-idling on root sync-noidle tree.
-
-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.