cfq-iosched: reimplement priorities using different service trees
We use different service trees for different priority classes.
This allows a simplification in the service tree insertion code, that no
longer has to consider priority while walking the tree.
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c95c69e..6e5c3d7 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -134,15 +134,31 @@
};
/*
+ * Index in the service_trees.
+ * IDLE is handled separately, so it has negative index
+ */
+enum wl_prio_t {
+ IDLE_WORKLOAD = -1,
+ BE_WORKLOAD = 0,
+ RT_WORKLOAD = 1
+};
+
+/*
* Per block device queue structure
*/
struct cfq_data {
struct request_queue *queue;
/*
- * rr list of queues with requests and the count of them
+ * rr lists of queues with requests, onle rr for each priority class.
+ * Counts are embedded in the cfq_rb_root
*/
- struct cfq_rb_root service_tree;
+ struct cfq_rb_root service_trees[2];
+ struct cfq_rb_root service_tree_idle;
+ /*
+ * The priority currently being served
+ */
+ enum wl_prio_t serving_prio;
/*
* Each priority tree is sorted by next_request position. These
@@ -152,7 +168,6 @@
struct rb_root prio_trees[CFQ_PRIO_LISTS];
unsigned int busy_queues;
- unsigned int busy_rt_queues;
unsigned int busy_queues_avg[2];
int rq_in_driver[2];
@@ -205,6 +220,15 @@
unsigned long last_end_sync_rq;
};
+static struct cfq_rb_root *service_tree_for(enum wl_prio_t prio,
+ struct cfq_data *cfqd)
+{
+ if (prio == IDLE_WORKLOAD)
+ return &cfqd->service_tree_idle;
+
+ return &cfqd->service_trees[prio];
+}
+
enum cfqq_state_flags {
CFQ_CFQQ_FLAG_on_rr = 0, /* on round-robin busy list */
CFQ_CFQQ_FLAG_wait_request, /* waiting for a request */
@@ -249,6 +273,23 @@
#define cfq_log(cfqd, fmt, args...) \
blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)
+static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
+{
+ if (cfq_class_idle(cfqq))
+ return IDLE_WORKLOAD;
+ if (cfq_class_rt(cfqq))
+ return RT_WORKLOAD;
+ return BE_WORKLOAD;
+}
+
+static inline int cfq_busy_queues_wl(enum wl_prio_t wl, struct cfq_data *cfqd)
+{
+ if (wl == IDLE_WORKLOAD)
+ return cfqd->service_tree_idle.count;
+
+ return cfqd->service_trees[wl].count;
+}
+
static void cfq_dispatch_insert(struct request_queue *, struct request *);
static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
struct io_context *, gfp_t);
@@ -332,10 +373,7 @@
unsigned min_q, max_q;
unsigned mult = cfq_hist_divisor - 1;
unsigned round = cfq_hist_divisor / 2;
- unsigned busy = cfqd->busy_rt_queues;
-
- if (!rt)
- busy = cfqd->busy_queues - cfqd->busy_rt_queues;
+ unsigned busy = cfq_busy_queues_wl(rt, cfqd);
min_q = min(cfqd->busy_queues_avg[rt], busy);
max_q = max(cfqd->busy_queues_avg[rt], busy);
@@ -546,7 +584,7 @@
}
/*
- * The cfqd->service_tree holds all pending cfq_queue's that have
+ * The cfqd->service_trees holds all pending cfq_queue's that have
* requests waiting to be processed. It is sorted in the order that
* we will service the queues.
*/
@@ -556,9 +594,10 @@
struct rb_node **p, *parent;
struct cfq_queue *__cfqq;
unsigned long rb_key;
- struct cfq_rb_root *service_tree = &cfqd->service_tree;
+ struct cfq_rb_root *service_tree;
int left;
+ service_tree = service_tree_for(cfqq_prio(cfqq), cfqd);
if (cfq_class_idle(cfqq)) {
rb_key = CFQ_IDLE_DELAY;
parent = rb_last(&service_tree->rb);
@@ -587,7 +626,8 @@
/*
* same position, nothing more to do
*/
- if (rb_key == cfqq->rb_key)
+ if (rb_key == cfqq->rb_key &&
+ cfqq->service_tree == service_tree)
return;
cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
@@ -605,25 +645,14 @@
__cfqq = rb_entry(parent, struct cfq_queue, rb_node);
/*
- * sort RT queues first, we always want to give
- * preference to them. IDLE queues goes to the back.
- * after that, sort on the next service time.
+ * sort by key, that represents service time.
*/
- if (cfq_class_rt(cfqq) > cfq_class_rt(__cfqq))
+ if (time_before(rb_key, __cfqq->rb_key))
n = &(*p)->rb_left;
- else if (cfq_class_rt(cfqq) < cfq_class_rt(__cfqq))
+ else {
n = &(*p)->rb_right;
- else if (cfq_class_idle(cfqq) < cfq_class_idle(__cfqq))
- n = &(*p)->rb_left;
- else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))
- n = &(*p)->rb_right;
- else if (time_before(rb_key, __cfqq->rb_key))
- n = &(*p)->rb_left;
- else
- n = &(*p)->rb_right;
-
- if (n == &(*p)->rb_right)
left = 0;
+ }
p = n;
}
@@ -722,8 +751,7 @@
BUG_ON(cfq_cfqq_on_rr(cfqq));
cfq_mark_cfqq_on_rr(cfqq);
cfqd->busy_queues++;
- if (cfq_class_rt(cfqq))
- cfqd->busy_rt_queues++;
+
cfq_resort_rr_list(cfqd, cfqq);
}
@@ -748,8 +776,6 @@
BUG_ON(!cfqd->busy_queues);
cfqd->busy_queues--;
- if (cfq_class_rt(cfqq))
- cfqd->busy_rt_queues--;
}
/*
@@ -1003,10 +1029,12 @@
*/
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
- if (RB_EMPTY_ROOT(&cfqd->service_tree.rb))
- return NULL;
+ struct cfq_rb_root *service_tree =
+ service_tree_for(cfqd->serving_prio, cfqd);
- return cfq_rb_first(&cfqd->service_tree);
+ if (RB_EMPTY_ROOT(&service_tree->rb))
+ return NULL;
+ return cfq_rb_first(service_tree);
}
/*
@@ -1123,6 +1151,12 @@
if (CFQQ_SEEKY(cfqq))
return NULL;
+ /*
+ * Do not merge queues of different priority classes
+ */
+ if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
+ return NULL;
+
return cfqq;
}
@@ -1336,6 +1370,14 @@
expire:
cfq_slice_expired(cfqd, 0);
new_queue:
+ if (!new_cfqq) {
+ if (cfq_busy_queues_wl(RT_WORKLOAD, cfqd))
+ cfqd->serving_prio = RT_WORKLOAD;
+ else if (cfq_busy_queues_wl(BE_WORKLOAD, cfqd))
+ cfqd->serving_prio = BE_WORKLOAD;
+ else
+ cfqd->serving_prio = IDLE_WORKLOAD;
+ }
cfqq = cfq_set_active_queue(cfqd, new_cfqq);
keep_queue:
return cfqq;
@@ -1362,8 +1404,12 @@
{
struct cfq_queue *cfqq;
int dispatched = 0;
+ int i;
+ for (i = 0; i < 2; ++i)
+ while ((cfqq = cfq_rb_first(&cfqd->service_trees[i])) != NULL)
+ dispatched += __cfq_forced_dispatch_cfqq(cfqq);
- while ((cfqq = cfq_rb_first(&cfqd->service_tree)) != NULL)
+ while ((cfqq = cfq_rb_first(&cfqd->service_tree_idle)) != NULL)
dispatched += __cfq_forced_dispatch_cfqq(cfqq);
cfq_slice_expired(cfqd, 0);
@@ -2710,7 +2756,9 @@
if (!cfqd)
return NULL;
- cfqd->service_tree = CFQ_RB_ROOT;
+ for (i = 0; i < 2; ++i)
+ cfqd->service_trees[i] = CFQ_RB_ROOT;
+ cfqd->service_tree_idle = CFQ_RB_ROOT;
/*
* Not strictly needed (since RB_ROOT just clears the node and we
