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From: Andi Kleen <>
Subject: [PATCH] Support worst case cache line sizes as config option
Date: Sun, 27 Apr 2003 04:23:46 +0200	[thread overview]
Message-ID: <20030427022346.GA27933@averell> (raw)

This mirrors a change that has been in the SuSE/aa 2.4 kernel for a long time.

For a generic binary kernel you really want to assume the worst case
cache line size.  That's the P4's 128 byte currently.

The overhead of having the cache line size bigger on other CPUs is not
that bad, but if it is too small it will cost you dearly on SMP and
even a bit on UP in device drivers. 

This patch adds a new CONFIG_X86_GENERIC option for this. It currently
only forces 128byte cache lines, but could be used for more in the future.

diff -u linux-gencpu/arch/i386/Kconfig-o linux-gencpu/arch/i386/Kconfig
--- linux-gencpu/arch/i386/Kconfig-o	2003-04-27 02:40:32.000000000 +0200
+++ linux-gencpu/arch/i386/Kconfig	2003-04-27 03:50:08.000000000 +0200
@@ -273,6 +273,13 @@
+config X86_GENERIC
+       bool "Generic x86 support" 
+       help
+       	  Include some tuning for non selected x86 CPUs too.
+	  when it has moderate overhead. This is intended for generic 
+	  distributions kernels.
 # Define implied options from the CPU selection here
@@ -288,10 +295,10 @@
 config X86_L1_CACHE_SHIFT
+	default "7" if MPENTIUM4 || X86_GENERIC
 	default "4" if MELAN || M486 || M386
 	default "5" if MWINCHIP3D || MWINCHIP2 || MWINCHIPC6 || MCRUSOE || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2
 	default "6" if MK7 || MK8
-	default "7" if MPENTIUM4

             reply	other threads:[~2003-04-27  2:11 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-04-27  2:23 Andi Kleen [this message]
     [not found] ` <BKEGKPICNAKILKJKMHCAAEPNCIAA.Riley@Williams.Name>
2003-04-27 12:52   ` [PATCH] Support worst case cache line sizes as config option Andi Kleen
2003-04-28  9:16 ` Adrian Bunk
2003-04-28 11:47   ` Andi Kleen
2003-04-28 12:19     ` Adrian Bunk
2003-04-28 12:48       ` Jamie Lokier
2003-04-28 22:00       ` Andi Kleen

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