diff mbox series

[v2,05/13] powerpc: use linux/unaligned/le_struct.h on LE power7

Message ID 20210514100106.3404011-6-arnd@kernel.org
State New
Headers show
Series Unify asm/unaligned.h around struct helper | expand

Commit Message

Arnd Bergmann May 14, 2021, 10 a.m. UTC
From: Arnd Bergmann <arnd@arndb.de>

Little-endian POWER7 kernels disable
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS because that is not supported on
the hardware, but the kernel still uses direct load/store for explicti
get_unaligned()/put_unaligned().

I assume this is a mistake that leads to power7 having to trap and fix
up all these unaligned accesses at a noticeable performance cost.

The fix is completely trivial, just remove the file and use the
generic version that gets it right.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/powerpc/include/asm/unaligned.h | 22 ----------------------
 1 file changed, 22 deletions(-)
 delete mode 100644 arch/powerpc/include/asm/unaligned.h

Comments

Segher Boessenkool May 14, 2021, 11:48 a.m. UTC | #1
Hi Arnd,

On Fri, May 14, 2021 at 12:00:53PM +0200, Arnd Bergmann wrote:
> Little-endian POWER7 kernels disable
> CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS because that is not supported on
> the hardware, but the kernel still uses direct load/store for explicti
> get_unaligned()/put_unaligned().
> 
> I assume this is a mistake that leads to power7 having to trap and fix
> up all these unaligned accesses at a noticeable performance cost.
> 
> The fix is completely trivial, just remove the file and use the
> generic version that gets it right.

LE p7 isn't supported (it requires special firmware), and no one uses it
anymore, also not for development.  It was used for powerpc64le-linux
development before p8 was widely available.


Segher
Arnd Bergmann May 14, 2021, 1:02 p.m. UTC | #2
On Fri, May 14, 2021 at 1:48 PM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Fri, May 14, 2021 at 12:00:53PM +0200, Arnd Bergmann wrote:
> > Little-endian POWER7 kernels disable
> > CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS because that is not supported on
> > the hardware, but the kernel still uses direct load/store for explicti
> > get_unaligned()/put_unaligned().
> >
> > I assume this is a mistake that leads to power7 having to trap and fix
> > up all these unaligned accesses at a noticeable performance cost.
> >
> > The fix is completely trivial, just remove the file and use the
> > generic version that gets it right.
>
> LE p7 isn't supported (it requires special firmware), and no one uses it
> anymore, also not for development.  It was used for powerpc64le-linux
> development before p8 was widely available.

Ok, thanks for the clarification.

Should we just remove the Kconfig option for it then as further cleanup?
Is there any other code such as alignment trap handling that could be
removed if LE POWER7 gets dropped?

      Arnd
diff mbox series

Patch

diff --git a/arch/powerpc/include/asm/unaligned.h b/arch/powerpc/include/asm/unaligned.h
deleted file mode 100644
index ce69c5eff95e..000000000000
--- a/arch/powerpc/include/asm/unaligned.h
+++ /dev/null
@@ -1,22 +0,0 @@ 
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_POWERPC_UNALIGNED_H
-#define _ASM_POWERPC_UNALIGNED_H
-
-#ifdef __KERNEL__
-
-/*
- * The PowerPC can do unaligned accesses itself based on its endian mode.
- */
-#include <linux/unaligned/access_ok.h>
-#include <linux/unaligned/generic.h>
-
-#ifdef __LITTLE_ENDIAN__
-#define get_unaligned	__get_unaligned_le
-#define put_unaligned	__put_unaligned_le
-#else
-#define get_unaligned	__get_unaligned_be
-#define put_unaligned	__put_unaligned_be
-#endif
-
-#endif	/* __KERNEL__ */
-#endif	/* _ASM_POWERPC_UNALIGNED_H */