Re: [PATCH 0/5] ppc RT: Realtime preempt support for PPC

[Frank Rowand <frowand@mvista.com>]

Ingo Molnar wrote:
> * Frank Rowand <frowand@mvista.com> wrote:
>
>
> > < more stuff deleted >
> >
> > I'm working on the architecture support for realtime on PPC64 now. If 
> > the lock field of struct raw_rwlock_t is a long instead of int then 
> > /proc/meminfo shows MemFree decreasing from 485608 kB to 485352 kB.
> >
> > Do you have a preference for lock to be long instead of int?
> >
> > Do you know if any of the other 64 bit architectures would have an 
> > issue with int?
>
>
> that would be nice to know. I have no preference, other than if possible 
> it should be unified, no #ifdefs or other conditionals.
>
> 	Ingo

I looked at all the architectures and found that the disparity of the
type of the "lock" field in struct rwlock_t is even larger than I had
indicated in my earlier email.  I am attaching a proof of concept patch
to handle this.  If this looks like a good method to you then I will
create a real patch against your current patch, and include i386,
mips, x86_64, and ppc.


Index: linux-2.6.10/include/linux/rt_lock.h
===================================================================
--- linux-2.6.10.orig/include/linux/rt_lock.h
+++ linux-2.6.10/include/linux/rt_lock.h
@@ -37,8 +37,9 @@ typedef struct {
  * but only one writer.
  */
 #ifdef CONFIG_SMP
+#include <asm/raw_spinlock.h>
 typedef struct {
-       volatile unsigned long lock;
+       ARCH_RAW_RWLOCK_LOCK
 # ifdef CONFIG_DEBUG_SPINLOCK
        unsigned magic;
 # endif
Index: linux-2.6.10/include/asm-ppc/raw_spinlock.h
===================================================================
--- /dev/null
+++ linux-2.6.10/include/asm-ppc/raw_spinlock.h
@@ -0,0 +1,6 @@
+#ifndef __ASM_RAW_SPINLOCK_H
+#define __ASM_RAW_SPINLOCK_H
+
+#define ARCH_RAW_RWLOCK_LOCK volatile signed int lock;
+
+#endif /* __ASM_RAW_SPINLOCK_H */
Index: linux-2.6.10/include/asm-i386/raw_spinlock.h
===================================================================
--- /dev/null
+++ linux-2.6.10/include/asm-i386/raw_spinlock.h
@@ -0,0 +1,6 @@
+#ifndef __ASM_RAW_SPINLOCK_H
+#define __ASM_RAW_SPINLOCK_H
+
+#define ARCH_RAW_RWLOCK_LOCK volatile unsigned int lock;
+
+#endif /* __ASM_RAW_SPINLOCK_H */




For the curious, the implementations of the "lock" field are listed
below:


rwlock_t lock implemented as a spinlock field and a counter field

   include/asm-parisc/spinlock.h
   include/asm-sh/spinlock.h

rwlock_t lock implemented as a 31 bit counter field and a 1 bit write lock field
   include/asm-ia64/spinlock.h

rwlock_t lock implemented as a 1 bit write lock field and a 31 bit counter field
   include/asm-alpha/spinlock.h

rwlock_t lock implemented as an unsigned int field

   include/asm-arm/spinlock.h
   include/asm-i386/spinlock.h
   include/asm-mips/spinlock.h
   include/asm-x86_64/spinlock.h
   include/asm-sparc/spinlock.h
   include/asm-sparc64/spinlock.h #ifdef CONFIG_DEBUG_SPINLOCK

rwlock_t lock implemented as a signed int field

   include/asm-m32r/spinlock.h
   include/asm-ppc64/spinlock.h
   include/asm-ppc/spinlock.h

rwlock_t lock implemented as an unsigned long field

   include/asm-s390/spinlock.h

rwlock_t lock implemented as an unsigned int (_not_ in a structure)

   include/asm-sparc64/spinlock.h #ifdef CONFIG_DEBUG_SPINLOCK

SMP rwlock_t not supported (no SMP support)

   include/asm-arm26/spinlock.h
   include/asm-frv/spinlock.h
   include/asm-h8300/spinlock.h
   include/asm-m68knommu/spinlock.h
   include/asm-m68k/spinlock.h
   include/asm-sh64/spinlock.h


-Frank
--
Frank Rowand <frank_rowand@mvista.com>
MontaVista Software, Inc

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