+ sched-bitmap-size-accounting-fix.patch added to -mm tree

[akpm@xxxxxxxx]

The patch titled

     sched: bitmap size accounting fix

has been added to the -mm tree.  Its filename is

     sched-bitmap-size-accounting-fix.patch

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this


From: Steven Rostedt <rostedt@xxxxxxxxxxx>

sched.c has

#define BITMAP_SIZE ((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long))

and not

#define BITMAP_SIZE ((((MAX_PRIO)/8)+sizeof(long))/sizeof(long))

The MAX_PRIO+1 should really be just MAX_PRIO.

Priorities go from 0 to MAX_PRIO-1 so you only need to store MAX_PRIO bits.
 As you probably know since you define the array in the run queue to only
queue[MAX_PRIO] and not [MAX_PRIO+1].

So on a normal system where long is 4 bytes we get:

MAX_PRIO = 140
sizeof(long) = 4
((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long)) = 5

And with the new fix:

((((MAX_PRIO+7)/8)+sizeof(long)-1)/sizeof(long)) = 5

So the result is the same, and hence the "Silly" part in the subject.

But although this change really has no affect on the kernel, it is still a
correctness issue, and readability issue.  The +1+7 confuses people,
especially when the +1 is not needed.

Not to mention, for those that change the kernel to use their own priority
settings, it might waste one extra word (althought this is actually not
that big of a deal).

So for correctness and readability, I'm submitting this patch.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 kernel/sched.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -puN kernel/sched.c~sched-bitmap-size-accounting-fix kernel/sched.c
--- devel/kernel/sched.c~sched-bitmap-size-accounting-fix	2006-05-12 11:25:26.000000000 -0700
+++ devel-akpm/kernel/sched.c	2006-05-12 11:25:26.000000000 -0700
@@ -184,7 +184,7 @@ static unsigned int task_timeslice(task_
  * These are the runqueue data structures:
  */
 
-#define BITMAP_SIZE ((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long))
+#define BITMAP_SIZE ((((MAX_PRIO+7)/8)+sizeof(long)-1)/sizeof(long))
 
 typedef struct runqueue runqueue_t;
 
_

Patches currently in -mm which might be from rostedt@xxxxxxxxxxx are

fix-for-serial-uart-lockup.patch
jbd-avoid-kfree-null.patch
ext3_clear_inode-avoid-kfree-null.patch
sched-bitmap-size-accounting-fix.patch
rtmutex-remove-buggy-bug_on-in-pi-boosting-code.patch
document-futex-pi-design.patch

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