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Date: Fri, 21 Oct 2005 01:26:58 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@osdl.org>
Cc: torvalds@osdl.org, arjan@infradead.org, dada1@cosmosbay.com,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] i386 spinlocks should use the full 32 bits, not only 8 bits
Message-ID: <20051020232658.GA29923@elte.hu>
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* Andrew Morton <akpm@osdl.org> wrote:

> > > spin_lock is still uninlined.
> > 
> > yes, and that should stay so i believe, for text size reasons. The BTB 
> > should eliminate most effects of the call+ret itself.
> 
> The old
> 
> 	lock; decb
> 	js <different section>
> 	...
> 
> was pretty good.

yes, but that's 4-7+6==10-13 bytes of inline footprint, compared to 
fixed 5 bytes. That gives quite some icache footprint with thousands of 
call sites.

> > hm, with my patch, write_unlock should be inlined too.
> 
> So it is.  foo_unlock_irq() isn't though.

yes, that one should probably be inlined too, it's just 1 byte longer, 
still the network-effects on register allocations give a net win:

    text    data     bss     dec     hex filename
 4072031  858208  387196 5317435  51233b vmlinux-smp-uninlined
 4060671  858212  387196 5306079  50f6df vmlinux-smp-inlined
 4058543  858212  387196 5303951  50ee8f vmlinux-irqop-inlined-too

another 0.05% drop in text size. Add-on patch below, it is against -rc5 
plus prev_spinlock_patch. Boot-tested on 4-way x86 SMP. The box crashed 
and burned. Joking.

	Ingo

 include/linux/spinlock.h |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

Index: linux/include/linux/spinlock.h
===================================================================
--- linux.orig/include/linux/spinlock.h
+++ linux/include/linux/spinlock.h
@@ -184,19 +184,29 @@ extern int __lockfunc generic__raw_read_
 # define write_unlock(lock)		__raw_write_unlock(&(lock)->raw_lock)
 #endif
 
+#if defined(CONFIG_DEBUG_SPINLOCK) || defined(CONFIG_PREEMPT)
+# define spin_unlock_irq(lock)		_spin_unlock_irq(lock)
+# define read_unlock_irq(lock)		_read_unlock_irq(lock)
+# define write_unlock_irq(lock)		_write_unlock_irq(lock)
+#else
+# define spin_unlock_irq(lock) \
+    do { __raw_spin_unlock(&(lock)->raw_lock); local_irq_enable(); } while (0)
+# define read_unlock_irq(lock) \
+    do { __raw_read_unlock(&(lock)->raw_lock); local_irq_enable(); } while (0)
+# define write_unlock_irq(lock) \
+    do { __raw_write_unlock(&(lock)->raw_lock); local_irq_enable(); } while (0)
+#endif
+
 #define spin_unlock_irqrestore(lock, flags) \
 					_spin_unlock_irqrestore(lock, flags)
-#define spin_unlock_irq(lock)		_spin_unlock_irq(lock)
 #define spin_unlock_bh(lock)		_spin_unlock_bh(lock)
 
 #define read_unlock_irqrestore(lock, flags) \
 					_read_unlock_irqrestore(lock, flags)
-#define read_unlock_irq(lock)		_read_unlock_irq(lock)
 #define read_unlock_bh(lock)		_read_unlock_bh(lock)
 
 #define write_unlock_irqrestore(lock, flags) \
 					_write_unlock_irqrestore(lock, flags)
-#define write_unlock_irq(lock)		_write_unlock_irq(lock)
 #define write_unlock_bh(lock)		_write_unlock_bh(lock)
 
 #define spin_trylock_bh(lock)		__cond_lock(_spin_trylock_bh(lock))
-
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