[PATCH 1/2] powerpc: Only disable HAVE_EFFICIENT_UNALIGNED_ACCESS on POWER7 little endian

From: Anton Blanchard <redacted>

POWER8 handles unaligned accesses in little endian mode, but commit
0b5e6661ac69 ("powerpc: Don't set HAVE_EFFICIENT_UNALIGNED_ACCESS on
little endian builds") disabled it for all.

The issue with unaligned little endian accesses is specific to POWER7,
so update the Kconfig check to match. Using the stat() testcase from
commit a75c380c7129 ("powerpc: Enable DCACHE_WORD_ACCESS on ppc64le"),
performance improves 15% on POWER8.

Signed-off-by: Anton Blanchard <redacted>
---
 arch/powerpc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 0a70c86..04c447d 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -96,7 +96,7 @@ config PPC
 	select VIRT_TO_BUS if !PPC64
 	select HAVE_IDE
 	select HAVE_IOREMAP_PROT
-	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_LITTLE_ENDIAN
+	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
 	select HAVE_KPROBES
 	select HAVE_ARCH_KGDB
 	select HAVE_KRETPROBES

-- 
2.7.4

From: Anton Blanchard <redacted>

We supported POWER7 CPUs for bootstrapping little endian, but the
target was always POWER8. Now that POWER7 specific issues are
impacting performance, change the default target to POWER8.

Signed-off-by: Anton Blanchard <redacted>
---
 arch/powerpc/platforms/Kconfig.cputype | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index f32edec..fa06676 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -86,6 +86,7 @@ endchoice
 choice
 	prompt "CPU selection"
 	depends on PPC64
+	default POWER8_CPU if CPU_LITTLE_ENDIAN
 	default GENERIC_CPU
 	help
 	  This will create a kernel which is optimised for a particular CPU.

-- 
2.7.4

On Sun, 2016-09-25 at 22:35 +1000, Anton Blanchard wrote:

From: Anton Blanchard <redacted>

POWER8 handles unaligned accesses in little endian mode, but commit
0b5e6661ac69 ("powerpc: Don't set HAVE_EFFICIENT_UNALIGNED_ACCESS on
little endian builds") disabled it for all.

The issue with unaligned little endian accesses is specific to
POWER7,
so update the Kconfig check to match. Using the stat() testcase from
commit a75c380c7129 ("powerpc: Enable DCACHE_WORD_ACCESS on
ppc64le"),
performance improves 15% on POWER8.

Hrm.. this should really be a runtime switch...

Hi Ben,

Hrm.. this should really be a runtime switch...

I wonder if anyone is still running POWER7 LE, perhaps we could drop it
entirely.

Anton

On Sun, 2016-25-09 at 12:35:40 UTC, Anton Blanchard wrote:

From: Anton Blanchard <redacted>

POWER8 handles unaligned accesses in little endian mode, but commit
0b5e6661ac69 ("powerpc: Don't set HAVE_EFFICIENT_UNALIGNED_ACCESS on
little endian builds") disabled it for all.

The issue with unaligned little endian accesses is specific to POWER7,
so update the Kconfig check to match. Using the stat() testcase from
commit a75c380c7129 ("powerpc: Enable DCACHE_WORD_ACCESS on ppc64le"),
performance improves 15% on POWER8.

Signed-off-by: Anton Blanchard <redacted>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/8a18cc0c2c36ee49d70a620ac0190d

cheers