Commit b4627321 authored by Vivek Goyal's avatar Vivek Goyal Committed by Jens Axboe

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

- 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
Reported-by: default avatarAndi Kleen <>
Signed-off-by: default avatarVivek Goyal <>
Acked-by: default avatarJeff Moyer <>
Signed-off-by: default avatarJens Axboe <>
parent 11a691be
......@@ -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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