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| author | Justin TerAvest <teravest@google.com> | 2011-03-01 15:05:08 -0500 |
|---|---|---|
| committer | Jens Axboe <jaxboe@fusionio.com> | 2011-03-01 15:05:08 -0500 |
| commit | 0bbfeb8320421989d3e12bd95fae86b9ac0712aa (patch) | |
| tree | a23bb6686bd2586fe7c27d0773c63f9aeb254cd1 /Documentation | |
| parent | 6fae9c25134baffbeeb20031479e7ff6f6d8eec0 (diff) | |
| download | linux-0bbfeb8320421989d3e12bd95fae86b9ac0712aa.tar.gz linux-0bbfeb8320421989d3e12bd95fae86b9ac0712aa.tar.bz2 linux-0bbfeb8320421989d3e12bd95fae86b9ac0712aa.zip | |
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.txt | 28 |
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. |