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Subject[PATCH] cfq-iosched: Always provide group isolation.
Date
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>
---
Documentation/cgroups/blkio-controller.txt | 28 ---------------------
block/cfq-iosched.c | 37 +---------------------------
2 files changed, 1 insertions(+), 64 deletions(-)

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index 4ed7b5c..d915c16 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.
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7be4c79..64feb6d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -146,7 +146,6 @@ struct cfq_queue {
struct cfq_rb_root *service_tree;
struct cfq_queue *new_cfqq;
struct cfq_group *cfqg;
- struct cfq_group *orig_cfqg;
/* Number of sectors dispatched from queue in single dispatch round */
unsigned long nr_sectors;
};
@@ -285,7 +284,6 @@ struct cfq_data {
unsigned int cfq_slice_idle;
unsigned int cfq_group_idle;
unsigned int cfq_latency;
- unsigned int cfq_group_isolation;

unsigned int cic_index;
struct list_head cic_list;
@@ -1187,32 +1185,6 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
int new_cfqq = 1;
int group_changed = 0;

-#ifdef CONFIG_CFQ_GROUP_IOSCHED
- if (!cfqd->cfq_group_isolation
- && cfqq_type(cfqq) == SYNC_NOIDLE_WORKLOAD
- && cfqq->cfqg && cfqq->cfqg != &cfqd->root_group) {
- /* Move this cfq to root group */
- cfq_log_cfqq(cfqd, cfqq, "moving to root group");
- if (!RB_EMPTY_NODE(&cfqq->rb_node))
- cfq_group_service_tree_del(cfqd, cfqq->cfqg);
- cfqq->orig_cfqg = cfqq->cfqg;
- cfqq->cfqg = &cfqd->root_group;
- cfqd->root_group.ref++;
- group_changed = 1;
- } else if (!cfqd->cfq_group_isolation
- && cfqq_type(cfqq) == SYNC_WORKLOAD && cfqq->orig_cfqg) {
- /* cfqq is sequential now needs to go to its original group */
- BUG_ON(cfqq->cfqg != &cfqd->root_group);
- if (!RB_EMPTY_NODE(&cfqq->rb_node))
- cfq_group_service_tree_del(cfqd, cfqq->cfqg);
- cfq_put_cfqg(cfqq->cfqg);
- cfqq->cfqg = cfqq->orig_cfqg;
- cfqq->orig_cfqg = NULL;
- group_changed = 1;
- cfq_log_cfqq(cfqd, cfqq, "moved to origin group");
- }
-#endif
-
service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
cfqq_type(cfqq));
if (cfq_class_idle(cfqq)) {
@@ -2542,7 +2514,7 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
static void cfq_put_queue(struct cfq_queue *cfqq)
{
struct cfq_data *cfqd = cfqq->cfqd;
- struct cfq_group *cfqg, *orig_cfqg;
+ struct cfq_group *cfqg;

BUG_ON(cfqq->ref <= 0);

@@ -2554,7 +2526,6 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
BUG_ON(rb_first(&cfqq->sort_list));
BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
cfqg = cfqq->cfqg;
- orig_cfqg = cfqq->orig_cfqg;

if (unlikely(cfqd->active_queue == cfqq)) {
__cfq_slice_expired(cfqd, cfqq, 0);
@@ -2564,8 +2535,6 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
BUG_ON(cfq_cfqq_on_rr(cfqq));
kmem_cache_free(cfq_pool, cfqq);
cfq_put_cfqg(cfqg);
- if (orig_cfqg)
- cfq_put_cfqg(orig_cfqg);
}

/*
@@ -3953,7 +3922,6 @@ static void *cfq_init_queue(struct request_queue *q)
cfqd->cfq_slice_idle = cfq_slice_idle;
cfqd->cfq_group_idle = cfq_group_idle;
cfqd->cfq_latency = 1;
- cfqd->cfq_group_isolation = 0;
cfqd->hw_tag = -1;
/*
* we optimistically start assuming sync ops weren't delayed in last
@@ -4029,7 +3997,6 @@ SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
-SHOW_FUNCTION(cfq_group_isolation_show, cfqd->cfq_group_isolation, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
@@ -4063,7 +4030,6 @@ STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
UINT_MAX, 0);
STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
-STORE_FUNCTION(cfq_group_isolation_store, &cfqd->cfq_group_isolation, 0, 1, 0);
#undef STORE_FUNCTION

#define CFQ_ATTR(name) \
@@ -4081,7 +4047,6 @@ static struct elv_fs_entry cfq_attrs[] = {
CFQ_ATTR(slice_idle),
CFQ_ATTR(group_idle),
CFQ_ATTR(low_latency),
- CFQ_ATTR(group_isolation),
__ATTR_NULL
};

--
1.7.3.1


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