Re: [PATCH] Make I/O schedulers optional (Was: Re: Kernel 2.6 size increase)

From: Bernardo Innocenti (bernie@develer.com)
Date: Sat Jul 26 2003 - 18:42:47 EST


On Saturday 26 July 2003 16:07, Jens Axboe wrote:

> > /*
> > * linux/drivers/block/as-iosched.c
> > *
> > - * Anticipatory & deadline i/o scheduler.
> > + * Anticipatory i/o scheduler.
> > *
> > * Copyright (C) 2002 Jens Axboe <axboe@suse.de>
> > * Nick Piggin <piggin@cyberone.com.au>
>
> Huh? What is that about? AS is deadline + anticipation. Good rule is not
> to make comment changes when you don't know your changes to be a fact.

Oops, I thought it was done by mistake :-)

By the way, this comment in as-iosched.c refers to a missing file:

 /*
  * See Documentation/as-iosched.txt
  */

Another issue: to make the I/O schedulers configurable, I had to
fiddle with ll_rw_blk.c, makiing it slightly harder to understand.

The MTD layer uses a nice registration-based API that makes adding
maps and chips very clean and easy.

Of course, implementing a similar registration infrastructure just
to select between two scheduling policies would be overkill.

Instead, I think it would be nice if the kernel provided some
generic API for registration of components, modules, strategies,
algorithms, etc.

It could be useful in several places, from crypto to network protocols.

Perhaps it could be done with kobjs and it should provide a way to find
an item by name.

> About making it selectable, I'm fine with it. Please send an updated
> patch.

Here it is:

--------------------------------------------------------------------------

Add kconfig options to allow excluding either or both the I/O schedulers.
Mostly useful for embedded systems (save ~13KB):

With my desktop PC (i386) kernel:

   text data bss dec hex filename
   2210707 475856 150444 2837007 2b4a0f vmlinux_with_ioscheds
   2197763 473446 150380 2821589 2b0dd5 vmlinux_without_ioscheds

With my uClinux (m68knommu) kernel:

   text data bss dec hex filename
   807760 47384 78884 934028 e408c linux_without_ioscheds
   819276 52460 78896 950632 e8168 linux_with_ioscheds

diff -Nru linux-2.6.0-test1.orig/drivers/block/Kconfig.iosched linux-2.6.0-test1-with_elevator_patch/drivers/block/Kconfig.iosched
--- linux-2.6.0-test1.orig/drivers/block/Kconfig.iosched 1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/Kconfig.iosched 2003-07-26 14:25:44.000000000 +0200
@@ -0,0 +1,8 @@
+config IOSCHED_AS
+ bool "Anticipatory I/O scheduler" if EMBEDDED
+ default y
+
+config IOSCHED_DEADLINE
+ bool "Deadline I/O scheduler" if EMBEDDED
+ default y
+
diff -Nru linux-2.6.0-test1.orig/drivers/block/Makefile linux-2.6.0-test1-with_elevator_patch/drivers/block/Makefile
--- linux-2.6.0-test1.orig/drivers/block/Makefile 2003-07-14 05:37:16.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/Makefile 2003-07-25 20:21:50.000000000 +0200
@@ -13,9 +13,10 @@
 # kblockd threads
 #
 
-obj-y := elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o \
- deadline-iosched.o as-iosched.o
+obj-y := elevator.o ll_rw_blk.o ioctl.o genhd.o scsi_ioctl.o
 
+obj-$(CONFIG_IOSCHED_AS) += as-iosched.o
+obj-$(CONFIG_IOSCHED_DEADLINE) += deadline-iosched.o
 obj-$(CONFIG_MAC_FLOPPY) += swim3.o
 obj-$(CONFIG_BLK_DEV_FD) += floppy.o
 obj-$(CONFIG_BLK_DEV_FD98) += floppy98.o
diff -Nru linux-2.6.0-test1.orig/drivers/block/as-iosched.c linux-2.6.0-test1-with_elevator_patch/drivers/block/as-iosched.c
--- linux-2.6.0-test1.orig/drivers/block/as-iosched.c 2003-07-14 05:28:54.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/as-iosched.c 2003-07-25 20:19:44.000000000 +0200
@@ -1832,6 +1832,7 @@
         .elevator_exit_fn = as_exit,
 
         .elevator_ktype = &as_ktype,
+ .elevator_name = "anticipatory scheduling",
 };
 
 EXPORT_SYMBOL(iosched_as);
diff -Nru linux-2.6.0-test1.orig/drivers/block/deadline-iosched.c linux-2.6.0-test1-with_elevator_patch/drivers/block/deadline-iosched.c
--- linux-2.6.0-test1.orig/drivers/block/deadline-iosched.c 2003-07-14 05:37:15.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/deadline-iosched.c 2003-07-25 20:20:53.000000000 +0200
@@ -941,6 +941,7 @@
         .elevator_exit_fn = deadline_exit,
 
         .elevator_ktype = &deadline_ktype,
+ .elevator_name = "deadline",
 };
 
 EXPORT_SYMBOL(iosched_deadline);
diff -Nru linux-2.6.0-test1.orig/drivers/block/elevator.c linux-2.6.0-test1-with_elevator_patch/drivers/block/elevator.c
--- linux-2.6.0-test1.orig/drivers/block/elevator.c 2003-07-14 05:36:48.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/elevator.c 2003-07-25 19:27:41.000000000 +0200
@@ -409,6 +409,7 @@
         .elevator_merge_req_fn = elevator_noop_merge_requests,
         .elevator_next_req_fn = elevator_noop_next_request,
         .elevator_add_req_fn = elevator_noop_add_request,
+ .elevator_name = "noop",
 };
 
 module_init(elevator_global_init);
diff -Nru linux-2.6.0-test1.orig/drivers/block/ll_rw_blk.c linux-2.6.0-test1-with_elevator_patch/drivers/block/ll_rw_blk.c
--- linux-2.6.0-test1.orig/drivers/block/ll_rw_blk.c 2003-07-14 05:30:40.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/drivers/block/ll_rw_blk.c 2003-07-25 19:27:02.000000000 +0200
@@ -1205,17 +1205,31 @@
 
 static int __make_request(request_queue_t *, struct bio *);
 
-static elevator_t *chosen_elevator = &iosched_as;
+static elevator_t *chosen_elevator =
+#if defined(CONFIG_IOSCHED_AS)
+ &iosched_as;
+#elif defined(CONFIG_IOSCHED_DEADLINE)
+ &iosched_deadline;
+#else
+ &elevator_noop;
+#endif
 
+#if defined(CONFIG_IOSCHED_AS) || defined(CONFIG_IOSCHED_DEADLINE)
 static int __init elevator_setup(char *str)
 {
+#ifdef CONFIG_IOSCHED_DEADLINE
         if (!strcmp(str, "deadline"))
                 chosen_elevator = &iosched_deadline;
+#endif
+#ifdef CONFIG_IOSCHED_AS
         if (!strcmp(str, "as"))
                 chosen_elevator = &iosched_as;
+#endif
         return 1;
 }
+
 __setup("elevator=", elevator_setup);
+#endif /* CONFIG_IOSCHED_AS || CONFIG_IOSCHED_DEADLINE */
 
 /**
  * blk_init_queue - prepare a request queue for use with a block device
@@ -1255,10 +1269,7 @@
 
         if (!printed) {
                 printed = 1;
- if (chosen_elevator == &iosched_deadline)
- printk("deadline elevator\n");
- else if (chosen_elevator == &iosched_as)
- printk("anticipatory scheduling elevator\n");
+ printk("Using %s elevator\n", chosen_elevator->elevator_name);
         }
 
         if ((ret = elevator_init(q, chosen_elevator))) {
diff -Nru linux-2.6.0-test1.orig/init/Kconfig linux-2.6.0-test1-with_elevator_patch/init/Kconfig
--- linux-2.6.0-test1.orig/init/Kconfig 2003-07-14 05:37:16.000000000 +0200
+++ linux-2.6.0-test1-with_elevator_patch/init/Kconfig 2003-07-26 14:25:48.000000000 +0200
@@ -141,6 +141,8 @@
           Disabling this option will cause the kernel to be built without
           support for epoll family of system calls.
 
+source "drivers/block/Kconfig.iosched"
+
 endmenu # General setup
 
 
diff -Nru linux-2.6.0-test1.orig/include/linux/elevator.h linux-2.6.0-test1/include/linux/elevator.h
--- linux-2.6.0-test1.orig/include/linux/elevator.h 2003-07-14 05:29:27.000000000 +0200
+++ linux-2.6.0-test1/include/linux/elevator.h 2003-07-25 19:18:39.000000000 +0200
@@ -52,6 +52,7 @@
 
         struct kobject kobj;
         struct kobj_type *elevator_ktype;
+ const char *elevator_name;
 };
 
 /*

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

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