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Date: Wed, 21 Jun 2006 22:59:32 +0200
From: Andreas Mohr <andi@rhlx01.fht-esslingen.de>
To: Andrew Morton <akpm@osdl.org>
Cc: Arjan van de Ven <arjan@infradead.org>,
       Nick Piggin <nickpiggin@yahoo.com.au>, linux-kernel@vger.kernel.org
Subject: [PATCH -mm 1/6] cpu_relax(): interrupt.h
Message-ID: <20060621205932.GA22516@rhlx01.fht-esslingen.de>
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Add cpu_relax() to tasklet_unlock_wait() loop.


I kept barrier() since it is said to still be required, in various older
postings.
Took care of kernel style formatting.

Tested on 2.6.17-mm1.


This is the first patch within a set, which aims to improve P4 HT performance
a bit:
these SMT CPUs want a rep nop (pause) (as done by cpu_relax()) when
busy-polling, in order to free pipeline resources for the SMT CPU sibling.

During I/O polling cpu_relax() will help for non-P4 CPUs, too (reduce
power consumption there).

Signed-off-by: Andreas Mohr <andi@lisas.de>


diff -urN linux-2.6.17-mm1.orig/include/linux/interrupt.h linux-2.6.17-mm1.my/include/linux/interrupt.h
--- linux-2.6.17-mm1.orig/include/linux/interrupt.h	2006-06-21 14:28:19.000000000 +0200
+++ linux-2.6.17-mm1.my/include/linux/interrupt.h	2006-06-21 21:34:12.000000000 +0200
@@ -227,7 +227,10 @@
 
 static inline void tasklet_unlock_wait(struct tasklet_struct *t)
 {
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		barrier();
+		cpu_relax();
+	}
 }
 #else
 #define tasklet_trylock(t) 1