[PATCH][noMMU] microblaze: allow PAGE_SIZE configuration

[Steven J. Magnani]

Allow developer to configure memory page size at compile time.
Larger pages can improve performance on some workloads.

Based on PowerPC code.

Signed-off-by: Steven J. Magnani <steve@xxxxxxxxxxxxxxx>
---
diff -uprN a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
--- a/arch/microblaze/include/asm/page.h	2010-05-13 09:55:59.000000000 -0500
+++ b/arch/microblaze/include/asm/page.h	2010-05-13 10:39:51.000000000 -0500
@@ -23,8 +23,16 @@
 #ifdef __KERNEL__
 
 /* PAGE_SHIFT determines the page size */
-#define PAGE_SHIFT	(12)
-#define PAGE_SIZE	(_AC(1, UL) << PAGE_SHIFT)
+#if defined(CONFIG_MICROBLAZE_32K_PAGES)
+#define PAGE_SHIFT		15
+#elif defined(CONFIG_MICROBLAZE_16K_PAGES)
+#define PAGE_SHIFT		14
+#elif defined(CONFIG_MICROBLAZE_8K_PAGES)
+#define PAGE_SHIFT		13
+#else
+#define PAGE_SHIFT		12
+#endif
+#define PAGE_SIZE	(ASM_CONST(1) << PAGE_SHIFT)
 #define PAGE_MASK	(~(PAGE_SIZE-1))
 
 #define LOAD_OFFSET	ASM_CONST((CONFIG_KERNEL_START-CONFIG_KERNEL_BASE_ADDR))
diff -uprN a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
--- a/arch/microblaze/Kconfig	2010-05-13 09:55:59.000000000 -0500
+++ b/arch/microblaze/Kconfig	2010-05-13 10:39:16.000000000 -0500
@@ -223,6 +223,36 @@ config TASK_SIZE
 	hex "Size of user task space" if TASK_SIZE_BOOL
 	default "0x80000000"
 
+choice
+	prompt "Page size"
+	default MICROBLAZE_4K_PAGES
+	depends on ADVANCED_OPTIONS
+	help
+	  Select the kernel logical page size. Increasing the page size
+	  will reduce software overhead at each page boundary, allow
+	  hardware prefetch mechanisms to be more effective, and allow
+	  larger dma transfers increasing IO efficiency and reducing
+	  overhead. However the utilization of memory will increase.
+	  For example, each cached file will using a multiple of the
+	  page size to hold its contents and the difference between the
+	  end of file and the end of page is wasted.
+
+	  If unsure, choose 4K_PAGES.
+
+config MICROBLAZE_4K_PAGES
+	bool "4k page size"
+
+config MICROBLAZE_8K_PAGES
+	bool "8k page size" if !MMU
+
+config MICROBLAZE_16K_PAGES
+	bool "16k page size" if !MMU
+
+config MICROBLAZE_32K_PAGES
+	bool "32k page size" if !MMU
+
+endchoice
+
 endmenu
 
 source "mm/Kconfig"
diff -uprN a/arch/microblaze/kernel/cpu/mb.c b/arch/microblaze/kernel/cpu/mb.c
--- a/arch/microblaze/kernel/cpu/mb.c	2010-05-13 09:55:59.000000000 -0500
+++ b/arch/microblaze/kernel/cpu/mb.c	2010-05-13 10:40:38.000000000 -0500
@@ -126,6 +126,7 @@ static int show_cpuinfo(struct seq_file 
 			cpuinfo.pvr_user1,
 			cpuinfo.pvr_user2);
 
+	count += seq_printf(m, "Page size:\t%lu\n", PAGE_SIZE);
 	return 0;
 }
 
diff -uprN a/arch/microblaze/kernel/vmlinux.lds.S b/arch/microblaze/kernel/vmlinux.lds.S
--- a/arch/microblaze/kernel/vmlinux.lds.S	2010-05-13 09:55:59.000000000 -0500
+++ b/arch/microblaze/kernel/vmlinux.lds.S	2010-05-10 15:32:30.000000000 -0500
@@ -55,7 +55,7 @@ SECTIONS {
 	 */
 	.sdata2 : AT(ADDR(.sdata2) - LOAD_OFFSET) {
 		_ssrw = .;
-		. = ALIGN(4096); /* page aligned when MMU used - origin 0x8 */
+		. = ALIGN(PAGE_SIZE); /* page aligned when MMU used */
 		*(.sdata2)
 	. = ALIGN(8);
 	_essrw = .;
@@ -70,7 +70,7 @@ SECTIONS {
 	/* Reserve some low RAM for r0 based memory references */
 	. = ALIGN(0x4) ;
 	r0_ram = . ;
-	. = . +  4096;	/* a page should be enough */
+	. = . +  PAGE_SIZE;	/* a page should be enough */
 
 	/* Under the microblaze ABI, .sdata and .sbss must be contiguous */
 	. = ALIGN(8);
@@ -120,7 +120,7 @@ SECTIONS {
 
 	__init_end_before_initramfs = .;
 
-	.init.ramfs ALIGN(4096) : AT(ADDR(.init.ramfs) - LOAD_OFFSET) {
+	.init.ramfs ALIGN(PAGE_SIZE) : AT(ADDR(.init.ramfs) - LOAD_OFFSET) {
 		__initramfs_start = .;
 		*(.init.ramfs)
 		__initramfs_end = .;
@@ -132,11 +132,11 @@ SECTIONS {
  * so that __init_end == __bss_start. This will make image.elf
  * consistent with the image.bin
  */
-		/* . = ALIGN(4096); */
+		/* . = ALIGN(PAGE_SIZE); */
 	}
 	__init_end = .;
 
-	.bss ALIGN (4096) : AT(ADDR(.bss) - LOAD_OFFSET) {
+	.bss ALIGN (PAGE_SIZE) : AT(ADDR(.bss) - LOAD_OFFSET) {
 		/* page aligned when MMU used */
 		__bss_start = . ;
 			*(.bss*)
@@ -145,7 +145,7 @@ SECTIONS {
 		__bss_stop = . ;
 		_ebss = . ;
 	}
-	. = ALIGN(4096);
+	. = ALIGN(PAGE_SIZE);
 	_end = .;
 
 	DISCARDS

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