Re: Large TLBs on 40x

On Tue, 2004-08-10 at 09:35, Matt Porter wrote:

On Tue, Aug 10, 2004 at 02:04:44AM -0400, Dan Malek wrote:

quoted

On Aug 9, 2004, at 10:21 PM, Josh Boyer wrote:

quoted

I have some boards I could test such a patch on.  Or is it a case of
"this isn't trivial to do"?

Ummmmm.....what are we talking about here?

Both MPC8xx, and IBM40x have configuration options for
pinning some (small) amount of kernel space.  You can choose
to enable this if you wish, I don't think it is normally enabled.
I've never found a benchmark that proved either was better,
but I left the code there for others to experiment with.

PPC40x no longer has this in 2.6. It has been deprecated by the dynamic
large tlb support. He's looking for an option (like nobats) to cause
kernel lowmem to not be mapped by large page entries.

So, to answer the original question, I would suggest a patch
that that uses a 'noltlb' cmdline option, then skips the PPC40x
large page mapping in 4xx_mmu.c based on that. See the code
that implements 'nobats' for an example.

Hm...  like this?  Against 2.6.8-rc4.

thx,
josh


diff -Naur -x '*.swp' linux-2.6.orig/arch/ppc/mm/4xx_mmu.c linux-2.6/arch/ppc/mm/4xx_mmu.c

--- linux-2.6.orig/arch/ppc/mm/4xx_mmu.c	2004-06-16 00:18:37.000000000 -0500
+++ linux-2.6/arch/ppc/mm/4xx_mmu.c	2004-08-11 08:25:11.000000000 -0500

@@ -52,6 +52,7 @@
 #include <asm/setup.h>
 #include "mmu_decl.h"

+extern int __map_without_ltlbs;
 /*
  * MMU_init_hw does the chip-specific initialization of the MMU hardware.
  */

@@ -102,6 +103,10 @@
 	p = PPC_MEMSTART;
 	s = 0;

+	if (__map_without_ltlbs) {
+		return s;
+	}
+
 	while (s <= (total_lowmem - LARGE_PAGE_SIZE_16M)) {
 		pmd_t *pmdp;
 		unsigned long val = p | _PMD_SIZE_16M | _PAGE_HWEXEC | _PAGE_HWWRITE;

diff -Naur -x '*.swp' linux-2.6.orig/arch/ppc/mm/init.c linux-2.6/arch/ppc/mm/init.c

--- linux-2.6.orig/arch/ppc/mm/init.c	2004-08-11 08:03:55.000000000 -0500
+++ linux-2.6/arch/ppc/mm/init.c	2004-08-11 08:11:24.000000000 -0500

@@ -104,6 +104,7 @@
  * -- Cort
  */
 int __map_without_bats;
+int __map_without_ltlbs;

 /* max amount of RAM to use */
 unsigned long __max_memory;

@@ -204,6 +205,10 @@
 		__map_without_bats = 1;
 	}

+	if (strstr(cmd_line, "noltlb")) {
+		__map_without_ltlbs = 1;
+	}
+
 	/* Look for mem= option on command line */
 	if (strstr(cmd_line, "mem=")) {
 		char *p, *q;

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