blk-cgroup: config options re-arrangement

This patch fixes few usability and configurability issues.

o All the cgroup based controller options are configurable from
  "Genral Setup/Control Group Support/" menu. blkio is the only exception.
  Hence make this option visible in above menu and make it configurable from
  there to bring it inline with rest of the cgroup based controllers.

o Get rid of CONFIG_DEBUG_CFQ_IOSCHED.

  This option currently does two things.

  - Enable printing of cgroup paths in blktrace
  - Enables CONFIG_DEBUG_BLK_CGROUP, which in turn displays additional stat
    files in cgroup.

  If we are using group scheduling, blktrace data is of not really much use
  if cgroup information is not present. To get this data, currently one has to
  also enable CONFIG_DEBUG_CFQ_IOSCHED, which in turn brings the overhead of
  all the additional debug stat files which is not desired.

  Hence, this patch moves printing of cgroup paths under
  CONFIG_CFQ_GROUP_IOSCHED.

  This allows us to get rid of CONFIG_DEBUG_CFQ_IOSCHED completely. Now all
  the debug stat files are controlled only by CONFIG_DEBUG_BLK_CGROUP which
  can be enabled through config menu.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Divyesh Shah <dpshah@google.com>
Reviewed-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Documentation/cgroups/blkio-controller.txt

@@ -17,6 +17,9 @@ HOWTO
 You can do a very simple testing of running two dd threads in two different
 cgroups. Here is what you can do.
 
+- Enable Block IO controller
+	CONFIG_BLK_CGROUP=y
+
 - Enable group scheduling in CFQ
 	CONFIG_CFQ_GROUP_IOSCHED=y
 
@@ -54,24 +57,16 @@ cgroups. Here is what you can do.
 
 Various user visible config options
 ===================================
-CONFIG_CFQ_GROUP_IOSCHED
-	- Enables group scheduling in CFQ. Currently only 1 level of group
-	  creation is allowed.
-
-CONFIG_DEBUG_CFQ_IOSCHED
-	- Enables some debugging messages in blktrace. Also creates extra
-	  cgroup file blkio.dequeue.
-
-Config options selected automatically
-=====================================
-These config options are not user visible and are selected/deselected
-automatically based on IO scheduler configuration.
-
 CONFIG_BLK_CGROUP
-	- Block IO controller. Selected by CONFIG_CFQ_GROUP_IOSCHED.
+	- Block IO controller.
 
 CONFIG_DEBUG_BLK_CGROUP
-	- Debug help. Selected by CONFIG_DEBUG_CFQ_IOSCHED.
+	- Debug help. Right now some additional stats file show up in cgroup
+	  if this option is enabled.
+
+CONFIG_CFQ_GROUP_IOSCHED
+	- Enables group scheduling in CFQ. Currently only 1 level of group
+	  creation is allowed.
 
 Details of cgroup files
 =======================
@@ -174,13 +169,13 @@ Details of cgroup files
 	  write, sync or async.
 
 - blkio.avg_queue_size
-	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
 	  The average queue size for this cgroup over the entire time of this
 	  cgroup's existence. Queue size samples are taken each time one of the
 	  queues of this cgroup gets a timeslice.
 
 - blkio.group_wait_time
-	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
 	  This is the amount of time the cgroup had to wait since it became busy
 	  (i.e., went from 0 to 1 request queued) to get a timeslice for one of
 	  its queues. This is different from the io_wait_time which is the
@@ -191,7 +186,7 @@ Details of cgroup files
 	  got a timeslice and will not include the current delta.
 
 - blkio.empty_time
-	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
 	  This is the amount of time a cgroup spends without any pending
 	  requests when not being served, i.e., it does not include any time
 	  spent idling for one of the queues of the cgroup. This is in
@@ -200,7 +195,7 @@ Details of cgroup files
 	  time it had a pending request and will not include the current delta.
 
 - blkio.idle_time
-	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y.
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y.
 	  This is the amount of time spent by the IO scheduler idling for a
 	  given cgroup in anticipation of a better request than the exising ones
 	  from other queues/cgroups. This is in nanoseconds. If this is read
@@ -209,7 +204,7 @@ Details of cgroup files
 	  the current delta.
 
 - blkio.dequeue
-	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This
+	- Debugging aid only enabled if CONFIG_DEBUG_BLK_CGROUP=y. This
 	  gives the statistics about how many a times a group was dequeued
 	  from service tree of the device. First two fields specify the major
 	  and minor number of the device and third field specifies the number

block/Kconfig

@@ -77,29 +77,6 @@ config BLK_DEV_INTEGRITY
 	T10/SCSI Data Integrity Field or the T13/ATA External Path
 	Protection.  If in doubt, say N.
 
-config BLK_CGROUP
-	tristate "Block cgroup support"
-	depends on CGROUPS
-	depends on CFQ_GROUP_IOSCHED
-	default n
-	---help---
-	Generic block IO controller cgroup interface. This is the common
-	cgroup interface which should be used by various IO controlling
-	policies.
-
-	Currently, CFQ IO scheduler uses it to recognize task groups and
-	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

@@ -23,7 +23,8 @@ config IOSCHED_DEADLINE
 
 config IOSCHED_CFQ
 	tristate "CFQ I/O scheduler"
-	select BLK_CGROUP if CFQ_GROUP_IOSCHED
+	# If BLK_CGROUP is a module, CFQ has to be built as module.
+	depends on (BLK_CGROUP=m && m) || !BLK_CGROUP || BLK_CGROUP=y
 	default y
 	---help---
 	  The CFQ I/O scheduler tries to distribute bandwidth equally
@@ -33,22 +34,15 @@ config IOSCHED_CFQ
 
 	  This is the default I/O scheduler.
 
+	  Note: If BLK_CGROUP=m, then CFQ can be built only as module.
+
 config CFQ_GROUP_IOSCHED
 	bool "CFQ Group Scheduling support"
-	depends on IOSCHED_CFQ && CGROUPS
+	depends on IOSCHED_CFQ && BLK_CGROUP
 	default n
 	---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

@@ -351,10 +351,8 @@ 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
 	blkg->dev = dev;
 }
 EXPORT_SYMBOL_GPL(blkiocg_add_blkio_group);

block/blk-cgroup.h

@@ -108,10 +108,8 @@ 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
 	/* The device MKDEV(major, minor), this group has been created for */
 	dev_t dev;
 
@@ -147,6 +145,11 @@ struct blkio_policy_type {
 extern void blkio_policy_register(struct blkio_policy_type *);
 extern void blkio_policy_unregister(struct blkio_policy_type *);
 
+static inline char *blkg_path(struct blkio_group *blkg)
+{
+	return blkg->path;
+}
+
 #else
 
 struct blkio_group {
@@ -158,6 +161,8 @@ struct blkio_policy_type {
 static inline void blkio_policy_register(struct blkio_policy_type *blkiop) { }
 static inline void blkio_policy_unregister(struct blkio_policy_type *blkiop) { }
 
+static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
+
 #endif
 
 #define BLKIO_WEIGHT_MIN	100
@@ -165,10 +170,6 @@ static inline void blkio_policy_unregister(struct blkio_policy_type *blkiop) { }
 #define BLKIO_WEIGHT_DEFAULT	500
 
 #ifdef CONFIG_DEBUG_BLK_CGROUP
-static inline char *blkg_path(struct blkio_group *blkg)
-{
-	return blkg->path;
-}
 void blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg);
 void blkiocg_update_dequeue_stats(struct blkio_group *blkg,
 				unsigned long dequeue);
@@ -197,7 +198,6 @@ BLKG_FLAG_FNS(idling)
 BLKG_FLAG_FNS(empty)
 #undef BLKG_FLAG_FNS
 #else
-static inline char *blkg_path(struct blkio_group *blkg) { return NULL; }
 static inline void blkiocg_update_avg_queue_size_stats(
 						struct blkio_group *blkg) {}
 static inline void blkiocg_update_dequeue_stats(struct blkio_group *blkg,

block/cfq-iosched.c

@@ -345,7 +345,7 @@ CFQ_CFQQ_FNS(deep);
 CFQ_CFQQ_FNS(wait_busy);
 #undef CFQ_CFQQ_FNS
 
-#ifdef CONFIG_DEBUG_CFQ_IOSCHED
+#ifdef CONFIG_CFQ_GROUP_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', \

init/Kconfig

@@ -612,6 +612,33 @@ config RT_GROUP_SCHED
 
 endif #CGROUP_SCHED
 
+config BLK_CGROUP
+	tristate "Block IO controller"
+	depends on CGROUPS && BLOCK
+	default n
+	---help---
+	Generic block IO controller cgroup interface. This is the common
+	cgroup interface which should be used by various IO controlling
+	policies.
+
+	Currently, CFQ IO scheduler uses it to recognize task groups and
+	control disk bandwidth allocation (proportional time slice allocation)
+	to such task groups.
+
+	This option only enables generic Block IO controller infrastructure.
+	One needs to also enable actual IO controlling logic in CFQ for it
+	to take effect. (CONFIG_CFQ_GROUP_IOSCHED=y).
+
+	See Documentation/cgroups/blkio-controller.txt for more information.
+
+config DEBUG_BLK_CGROUP
+	bool "Enable Block IO controller debugging"
+	depends on BLK_CGROUP
+	default n
+	---help---
+	Enable some debugging help. Currently it exports additional stat
+	files in a cgroup which can be useful for debugging.
+
 endif # CGROUPS
 
 config MM_OWNER