block: remove the anticipatory IO scheduler

AS is mostly a subset of CFQ, so there's little point in still
providing this separate IO scheduler. Hopefully at some point we
can get down to one single IO scheduler again, at least this brings
us closer by having only one intelligent IO scheduler.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/Kconfig.iosched

@@ -12,24 +12,14 @@ config IOSCHED_NOOP
 	  that do their own scheduling and require only minimal assistance from
 	  the kernel.
 
-config IOSCHED_AS
-	tristate "Anticipatory I/O scheduler"
-	default y
-	---help---
-	  The anticipatory I/O scheduler is generally a good choice for most
-	  environments, but is quite large and complex when compared to the
-	  deadline I/O scheduler, it can also be slower in some cases
-	  especially some database loads.
-
 config IOSCHED_DEADLINE
 	tristate "Deadline I/O scheduler"
 	default y
 	---help---
-	  The deadline I/O scheduler is simple and compact, and is often as
-	  good as the anticipatory I/O scheduler, and in some database
-	  workloads, better. In the case of a single process performing I/O to
-	  a disk at any one time, its behaviour is almost identical to the
-	  anticipatory I/O scheduler and so is a good choice.
+	  The deadline I/O scheduler is simple and compact. It will provide
+	  CSCAN service with FIFO expiration of requests, switching to
+	  a new point in the service tree and doing a batch of IO from there
+	  in case of expiry.
 
 config IOSCHED_CFQ
 	tristate "CFQ I/O scheduler"
@@ -47,9 +37,6 @@ choice
 	  Select the I/O scheduler which will be used by default for all
 	  block devices.
 
-	config DEFAULT_AS
-		bool "Anticipatory" if IOSCHED_AS=y
-
 	config DEFAULT_DEADLINE
 		bool "Deadline" if IOSCHED_DEADLINE=y
 
@@ -63,7 +50,6 @@ endchoice
 
 config DEFAULT_IOSCHED
 	string
-	default "anticipatory" if DEFAULT_AS
 	default "deadline" if DEFAULT_DEADLINE
 	default "cfq" if DEFAULT_CFQ
 	default "noop" if DEFAULT_NOOP

block/Makefile

@@ -9,7 +9,6 @@ obj-$(CONFIG_BLOCK) := elevator.o blk-core.o blk-tag.o blk-sysfs.o \
 
 obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o
 obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o
-obj-$(CONFIG_IOSCHED_AS)	+= as-iosched.o
 obj-$(CONFIG_IOSCHED_DEADLINE)	+= deadline-iosched.o
 obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 

block/elevator.c

@@ -154,10 +154,7 @@ static struct elevator_type *elevator_get(const char *name)
 
 		spin_unlock(&elv_list_lock);
 
-		if (!strcmp(name, "anticipatory"))
-			sprintf(elv, "as-iosched");
-		else
-			sprintf(elv, "%s-iosched", name);
+		sprintf(elv, "%s-iosched", name);
 
 		request_module("%s", elv);
 		spin_lock(&elv_list_lock);
@@ -193,10 +190,7 @@ static int __init elevator_setup(char *str)
 	 * Be backwards-compatible with previous kernels, so users
 	 * won't get the wrong elevator.
 	 */
-	if (!strcmp(str, "as"))
-		strcpy(chosen_elevator, "anticipatory");
-	else
-		strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
+	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
 	return 1;
 }