lkml.org 
[lkml]   [1999]   [Sep]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: possible spinlock optimizations
On Tue, 28 Sep 1999, Manfred wrote:

>1) spin_lock_irq(): What about enabling interrupts while spinning?

Looks a very good idea to me ;). I think it worth to do that as the
changes are minimal and we are going to waste some cpu cycle while
spinning anyway so we have all the time for running sti. I think the only
additional RL cost will be the cli run every time we exit from the slow
path (but the slow path is just sloww).

I implemented it on 2.3.18ac9. I am writing this with it applyed.

--- 2.3.18ac9/include/linux/spinlock.h.~1~ Tue Sep 28 02:57:39 1999
+++ 2.3.18ac9/include/linux/spinlock.h Tue Sep 28 15:41:57 1999
@@ -1,20 +1,30 @@
#ifndef __LINUX_SPINLOCK_H
#define __LINUX_SPINLOCK_H

+#ifdef __SMP__
+#include <asm/spinlock.h>
+#endif
+
/*
* These are the generic versions of the spinlocks and read-write
* locks..
*/
#define spin_lock_irqsave(lock, flags) do { local_irq_save(flags); spin_lock(lock); } while (0)
+#ifndef __HAVE_ARCH_SPIN_LOCK_IRQ
#define spin_lock_irq(lock) do { local_irq_disable(); spin_lock(lock); } while (0)
+#endif
#define spin_lock_bh(lock) do { local_bh_disable(); spin_lock(lock); } while (0)

#define read_lock_irqsave(lock, flags) do { local_irq_save(flags); read_lock(lock); } while (0)
+#ifndef __HAVE_ARCH_READ_LOCK_IRQ
#define read_lock_irq(lock) do { local_irq_disable(); read_lock(lock); } while (0)
+#endif
#define read_lock_bh(lock) do { local_bh_disable(); read_lock(lock); } while (0)

#define write_lock_irqsave(lock, flags) do { local_irq_save(flags); write_lock(lock); } while (0)
+#ifndef __HAVE_ARCH_WRITE_LOCK_IRQ
#define write_lock_irq(lock) do { local_irq_disable(); write_lock(lock); } while (0)
+#endif
#define write_lock_bh(lock) do { local_bh_disable(); write_lock(lock); } while (0)

#define spin_unlock_irqrestore(lock, flags) do { spin_unlock(lock); local_irq_restore(flags); } while (0)
@@ -29,10 +39,8 @@
#define write_unlock_irq(lock) do { write_unlock(lock); local_irq_enable(); } while (0)
#define write_unlock_bh(lock) do { write_unlock(lock); local_bh_enable(); } while (0)

-#ifdef __SMP__
-#include <asm/spinlock.h>

-#else /* !SMP */
+#ifndef __SMP__ /* !SMP */

#define DEBUG_SPINLOCKS 0 /* 0 == no debugging, 1 == maintain lock state, 2 == full debug */

--- 2.3.18ac9/include/asm-i386/spinlock.h Tue Sep 14 14:35:57 1999
+++ /tmp/spinlock.h Tue Sep 28 15:56:04 1999
@@ -35,6 +35,20 @@
"jmp 1b\n" \
".previous"

+#define spin_lock_irq_string \
+ "\n1:\t" \
+ "cli\n\t" \
+ "lock ; btsl $0,%0\n\t" \
+ "jc 2f\n" \
+ ".section .text.lock,\"ax\"\n" \
+ "2:\t" \
+ "sti\n\t" \
+ "3:\t" \
+ "testb $1,%0\n\t" \
+ "jne 3b\n\t" \
+ "jmp 1b\n" \
+ ".previous"
+
#define spin_unlock_string \
"lock ; btrl $0,%0"

@@ -43,6 +57,12 @@
spin_lock_string \
:"=m" (__dummy_lock(lock)))

+#define __HAVE_ARCH_SPIN_LOCK_IRQ
+#define spin_lock_irq(lock) \
+__asm__ __volatile__( \
+ spin_lock_irq_string \
+ :"=m" (__dummy_lock(lock)))
+
#define spin_unlock(lock) \
__asm__ __volatile__( \
spin_unlock_string \
@@ -85,6 +105,21 @@
".previous" \
:"=m" (__dummy_lock(&(rw)->lock)))

+#define __HAVE_ARCH_READ_LOCK_IRQ
+#define read_lock_irq(rw) \
+ asm volatile("\n1:\t" \
+ "cli\n\t" \
+ "lock ; incl %0\n\t" \
+ "js 2f\n" \
+ ".section .text.lock,\"ax\"\n" \
+ "2:\tlock ; decl %0\n" \
+ "sti\n\t" \
+ "3:\tcmpl $0,%0\n\t" \
+ "js 3b\n\t" \
+ "jmp 1b\n" \
+ ".previous" \
+ :"=m" (__dummy_lock(&(rw)->lock)))
+
#define read_unlock(rw) \
asm volatile("lock ; decl %0" \
:"=m" (__dummy_lock(&(rw)->lock)))
@@ -99,6 +134,25 @@
"3:\tlock ; btrl $31,%0\n" \
"4:\tcmp $0,%0\n\t" \
"jne 4b\n\t" \
+ "jmp 1b\n" \
+ ".previous" \
+ :"=m" (__dummy_lock(&(rw)->lock)))
+
+#define __HAVE_ARCH_WRITE_LOCK_IRQ
+#define write_lock_irq(rw) \
+ asm volatile("\n1:\t" \
+ "cli\n\t" \
+ "lock ; btsl $31,%0\n\t" \
+ "jc 4f\n" \
+ "2:\ttestl $0x7fffffff,%0\n\t" \
+ "jne 3f\n" \
+ ".section .text.lock,\"ax\"\n" \
+ "3:\tlock ; btrl $31,%0\n" \
+ "4:\t" \
+ "sti\n\t" \
+ "5:\t" \
+ "cmp $0,%0\n\t" \
+ "jne 5b\n\t" \
"jmp 1b\n" \
".previous" \
:"=m" (__dummy_lock(&(rw)->lock)))
Andrea


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:54    [from the cache]
©2003-2011 Jasper Spaans