[PATCH 0/2] ARC: fix the THREAD_SHIFT definition

[PATCH 0/2] ARC: fix the THREAD_SHIFT definition

[Min-Hua Chen]

Hi,

When I read the arch/arc code, I first found that the
definition of THREAD_SHIFT looks incorrect and the
description of 16KSTACKS looks confusing. I submit
these 2 small patches to address the issue I found.

Min-Hua Chen (2):
  ARC: fix incorrect THREAD_SHIFT definition
  ARC: rename 16KSTACKS to DEBUG_STACKS

 arch/arc/Kconfig.debug             | 7 ++++---
 arch/arc/include/asm/thread_info.h | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

-- 
2.34.1


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[PATCH 1/2] ARC: fix incorrect THREAD_SHIFT definition

[Min-Hua Chen]

Current definition of THREAD_SHIFT is (PAGE_SHIFT << THREAD_SIZE_ORDER)
look incorrect. It should be (PAGE_SHIFT + THREAD_SIZE_ORDER) because
the following equation should hold:

Say PAGE_SHIFT == 13 (as the default value in ARC)
THREAD_SIZE_ORDER == 1 (as CONFIG_16KSTACKS=y)

THREAD_SIZE == (1 << THREAD_SHIFT)
            == (1 << (PAGE_SHIFT + THREAD_SIZE_ORDER))
	    == (1 << 14)
	    == 16KB

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
---
 arch/arc/include/asm/thread_info.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h
index 6ba7fe417095..9f9dd021501c 100644
--- a/arch/arc/include/asm/thread_info.h
+++ b/arch/arc/include/asm/thread_info.h
@@ -22,7 +22,7 @@
 #endif
 
 #define THREAD_SIZE     (PAGE_SIZE << THREAD_SIZE_ORDER)
-#define THREAD_SHIFT	(PAGE_SHIFT << THREAD_SIZE_ORDER)
+#define THREAD_SHIFT	(PAGE_SHIFT + THREAD_SIZE_ORDER)
 
 #ifndef __ASSEMBLY__
 
-- 
2.34.1


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[PATCH 2/2] ARC: rename 16KSTACKS to DEBUG_STACKS

[Min-Hua Chen]

Rename 16KSTACKS to DEBUG_STACKS.

arch/arc/Kconfig.debug says that the default stack size is 8KB
and it will become 16KB stack if 16KSTACKS is set.

However, the stack size is based on PAGE_SIZE, and it is
configurable by CONFIG_ARC_PAGE_SIZE_16K or CONFIG_ARC_PAGE_SIZE_4K.

See arch/arc/include/uapi/asm/page.h:
/* PAGE_SHIFT determines the page size */
\#if defined(CONFIG_ARC_PAGE_SIZE_16K)
\#define PAGE_SHIFT 14
\#elif defined(CONFIG_ARC_PAGE_SIZE_4K)
\#define PAGE_SHIFT 12
\#else
\#define PAGE_SHIFT 13
\#endif

See arch/arc/include/asm/thread_info.h:
\#ifdef CONFIG_DEBUG_STACKS
\#define THREAD_SIZE_ORDER 1
\#else
\#define THREAD_SIZE_ORDER 0
\#endif

\#define THREAD_SIZE     (PAGE_SIZE << THREAD_SIZE_ORDER)
\#define THREAD_SHIFT	(PAGE_SHIFT + THREAD_SIZE_ORDER)

To make CONFIG_16KSTACKS less confusing, rename it to DEBUG_STACKS
(as it is defined in Kconfig.debug) and modify the Kconfig
description. No functional changes intended.

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
---
 arch/arc/Kconfig.debug             | 7 ++++---
 arch/arc/include/asm/thread_info.h | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arc/Kconfig.debug b/arch/arc/Kconfig.debug
index 45add86decd5..9a1e140605c4 100644
--- a/arch/arc/Kconfig.debug
+++ b/arch/arc/Kconfig.debug
@@ -1,10 +1,11 @@
 # SPDX-License-Identifier: GPL-2.0
 
-config 16KSTACKS
-	bool "Use 16Kb for kernel stacks instead of 8Kb"
+config DEBUG_STACKS
+	bool "Use double sized kernel stacks"
 	help
-	  If you say Y here the kernel will use a  16Kb stacksize for the
+	  If you say Y here the kernel will use a double sized stack for the
 	  kernel stack attached to each process/thread. The default is 8K.
+	  (depends on CONFIG_ARC_PAGE_SIZE_16K or CONFIG_ARC_PAGE_SIZE_4K)
 	  This increases the resident kernel footprint and will cause less
 	  threads to run on the system and also increase the pressure
 	  on the VM subsystem for higher order allocations.
diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h
index 9f9dd021501c..a7358d1225a6 100644
--- a/arch/arc/include/asm/thread_info.h
+++ b/arch/arc/include/asm/thread_info.h
@@ -15,7 +15,7 @@
 
 #include <asm/page.h>
 
-#ifdef CONFIG_16KSTACKS
+#ifdef CONFIG_DEBUG_STACKS
 #define THREAD_SIZE_ORDER 1
 #else
 #define THREAD_SIZE_ORDER 0
-- 
2.34.1


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