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 <ak@linux.intel.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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 @@
BE_WORKLOAD = 0,
RT_WORKLOAD = 1,
IDLE_WORKLOAD = 2,
+ CFQ_PRIO_NR,
};
/*
@@ -181,10 +182,19 @@
/* 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];