blkio: Some debugging aids for CFQ

o Some debugging aids for CFQ.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/Kconfig

@@ -90,6 +90,15 @@ config BLK_CGROUP
 	control disk bandwidth allocation (proportional time slice allocation)
 	to such task groups.
 
+config DEBUG_BLK_CGROUP
+	bool
+	depends on BLK_CGROUP
+	default n
+	---help---
+	Enable some debugging help. Currently it stores the cgroup path
+	in the blk group which can be used by cfq for tracing various
+	group related activity.
+
 endif # BLOCK
 
 config BLOCK_COMPAT

block/Kconfig.iosched

@@ -40,6 +40,15 @@ config CFQ_GROUP_IOSCHED
 	---help---
 	  Enable group IO scheduling in CFQ.
 
+config DEBUG_CFQ_IOSCHED
+	bool "Debug CFQ Scheduling"
+	depends on CFQ_GROUP_IOSCHED
+	select DEBUG_BLK_CGROUP
+	default n
+	---help---
+	  Enable CFQ IO scheduling debugging in CFQ. Currently it makes
+	  blktrace output more verbose.
+
 choice
 	prompt "Default I/O scheduler"
 	default DEFAULT_CFQ

block/blk-cgroup.c

@@ -33,6 +33,10 @@ void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
 	blkg->blkcg_id = css_id(&blkcg->css);
 	hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);
 	spin_unlock_irqrestore(&blkcg->lock, flags);
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+	/* Need to take css reference ? */
+	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
+#endif
 }
 
 static void __blkiocg_del_blkio_group(struct blkio_group *blkg)

block/blk-cgroup.h

@@ -27,12 +27,25 @@ struct blkio_group {
 	void *key;
 	struct hlist_node blkcg_node;
 	unsigned short blkcg_id;
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+	/* Store cgroup path */
+	char path[128];
+#endif
 };
 
 #define BLKIO_WEIGHT_MIN	100
 #define BLKIO_WEIGHT_MAX	1000
 #define BLKIO_WEIGHT_DEFAULT	500
 
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+static inline char *blkg_path(struct blkio_group *blkg)
+{
+	return blkg->path;
+}
+#else
+static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
+#endif
+
 #ifdef CONFIG_BLK_CGROUP
 extern struct blkio_cgroup blkio_root_cgroup;
 extern struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup);

block/cfq-iosched.c

@@ -341,8 +341,21 @@ CFQ_CFQQ_FNS(coop);
 CFQ_CFQQ_FNS(deep);
 #undef CFQ_CFQQ_FNS
 
+#ifdef CONFIG_DEBUG_CFQ_IOSCHED
+#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
+	blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
+			cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
+			blkg_path(&(cfqq)->cfqg->blkg), ##args);
+
+#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)				\
+	blk_add_trace_msg((cfqd)->queue, "%s " fmt,			\
+				blkg_path(&(cfqg)->blkg), ##args);      \
+
+#else
 #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)	\
 	blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
+#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)		do {} while (0);
+#endif
 #define cfq_log(cfqd, fmt, args...)	\
 	blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)
 
@@ -832,6 +845,7 @@ cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
 	if (cfqg->nr_cfqq)
 		return;
 
+	cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
 	cfqg->on_st = false;
 	cfqd->nr_groups--;
 	st->total_weight -= cfqg->weight;
@@ -889,6 +903,9 @@ static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
 		cfqg->saved_serving_prio = cfqd->serving_prio;
 	} else
 		cfqg->saved_workload_slice = 0;
+
+	cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
+					st->min_vdisktime);
 }
 
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
@@ -3102,7 +3119,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
 	unsigned long now;
 
 	now = jiffies;
-	cfq_log_cfqq(cfqd, cfqq, "complete");
+	cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d", !!rq_noidle(rq));
 
 	cfq_update_hw_tag(cfqd);