linux-kernel - Re: [patch 4/4] powerpc 2.6.21-rt1: reduce scheduling latency by changing tlb flush size

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Date:	Mon, 14 May 2007 15:38:39 +0900
From:	Tsutomu OWA <tsutomu.owa@...hiba.co.jp>
To:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, tglx@...utronix.de
Subject: Re: [patch 4/4] powerpc 2.6.21-rt1: reduce scheduling latency by changing tlb flush size


Oopps, Subject was wrong.... resending it.  Sorry.

To reduce scheduling latecy by changing tlb flush size to 1.
Since tlb flush on Celleb is done by calling (an) expensive hypervisor call(s), 
it takes a long time to flush tlbs and causes scheduing latency.

As I don't know how long it takes on other platforms, it would be better to 
enclose it within #ifdef CONFIG_PPC_CELLEB.

Signed-off-by: Tsutomu OWA <tsutomu.owa@...hiba.co.jp>
-- owa

diff -rup linux-2.6.21-rt1/include/asm-powerpc/tlbflush.h rt/include/asm-powerpc/tlbflush.h
--- linux-2.6.21-rt1/include/asm-powerpc/tlbflush.h	2007-04-26 12:08:32.000000000 +0900
+++ rt/include/asm-powerpc/tlbflush.h	2007-05-07 14:23:50.000000000 +0900
@@ -25,7 +25,11 @@ struct mm_struct;
 #include <linux/percpu.h>
 #include <asm/page.h>
 
+#ifdef CONFIG_PREEMPT_RT
+#define PPC64_TLB_BATCH_NR 1 /* Since tlb flush takes long time, reduce it to 1 when RT */
+#else
 #define PPC64_TLB_BATCH_NR 192
+#endif /* CONFIG_PREEMPT_RT */
 
 struct ppc64_tlb_batch {
 	unsigned long index;

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