path: root/block
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authorVivek Goyal <>2010-10-22 09:48:43 +0200
committerJens Axboe <>2010-10-22 09:48:43 +0200
commitb4627321e18582dcbdeb45d77df29d3177107c65 (patch)
treef494dae7f39f219d73aa9752dfd3844293d65f50 /block
parent11a691bea48887c27425cc40bf291e74c922df25 (diff)
cfq-iosched: Fix a gcc 4.5 warning and put some comments
- Andi encountedred following warning with gcc 4.5 linux/block/cfq-iosched.c: In function ‘cfq_dispatch_requests’: linux/block/cfq-iosched.c:2156:3: warning: array subscript is above array bounds - Warning happens due to following code. slice = group_slice * count / max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio], cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg)); gcc is complaining about cfqg->busy_queues_avg[] being indexed by CFQ prio classes (RT, BE and IDLE) while the array size is only 2. - At run time, we never access cfqg->busy_queues_avg[IDLE] and return from function before this code hits. - To fix warning increase the array size though it will remain unused. This patch also puts some comments to clarify some of the confusions. - I have taken Jens's patch and modified it a bit. - Compile tested with gcc 4.4 and boot tested. I don't have gcc 4.5 running, Andi can you please test it with gcc 4.5 to make sure it worked. Reported-by: Andi Kleen <> Signed-off-by: Vivek Goyal <> Acked-by: Jeff Moyer <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block')
1 files changed, 13 insertions, 3 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 86338d5..dfceb63 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -157,6 +157,7 @@ enum wl_prio_t {
@@ -181,10 +182,19 @@ struct cfq_group {
/* number of cfqq currently on this group */
int nr_cfqq;
- /* Per group busy queus average. Useful for workload slice calc. */
- unsigned int busy_queues_avg[2];
- * rr lists of queues with requests, onle rr for each priority class.
+ * Per group busy queus average. Useful for workload slice calc. We
+ * create the array for each prio class but at run time it is used
+ * only for RT and BE class and slot for IDLE class remains unused.
+ * This is primarily done to avoid confusion and a gcc warning.
+ */
+ unsigned int busy_queues_avg[CFQ_PRIO_NR];
+ /*
+ * rr lists of queues with requests. We maintain service trees for
+ * RT and BE classes. These trees are subdivided in subclasses
+ * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
+ * class there is no subclassification and all the cfq queues go on
+ * a single tree service_tree_idle.
* Counts are embedded in the cfq_rb_root
struct cfq_rb_root service_trees[2][3];
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