[net-next-2.6 PATCH] x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN

[net-next-2.6 PATCH] x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN

[Jeff Kirsher]

From: Alexander Duyck <alexander.h.duyck@intel.com>

This patch removes the CONFIG_MCORE2 check from around NET_IP_ALIGN.  It is
based on a suggestion from Andi Kleen.  The assumption is that there are
not any x86 cores where unaligned access is really slow, and this change
would allow for a performance improvement to still exist on configurations
that are not necessarily optimized for Core 2.

Cc: Andi Kleen <ak@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
---

 arch/x86/include/asm/system.h |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index b4293fc..1db9bd2 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -457,7 +457,6 @@ static inline void rdtsc_barrier(void)
 	alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
 }
 
-#ifdef CONFIG_MCORE2
 /*
  * We handle most unaligned accesses in hardware.  On the other hand
  * unaligned DMA can be quite expensive on some Nehalem processors.
@@ -465,5 +464,4 @@ static inline void rdtsc_barrier(void)
  * Based on this we disable the IP header alignment in network drivers.
  */
 #define NET_IP_ALIGN	0
-#endif
 #endif /* _ASM_X86_SYSTEM_H */

Re: [net-next-2.6 PATCH] x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN

[Stephen Hemminger]

On Thu, 01 Jul 2010 16:28:27 -0700
Jeff Kirsher <jeffrey.t.kirsher@intel.com> wrote:

> From: Alexander Duyck <alexander.h.duyck@intel.com>
> 
> This patch removes the CONFIG_MCORE2 check from around NET_IP_ALIGN.  It is
> based on a suggestion from Andi Kleen.  The assumption is that there are
> not any x86 cores where unaligned access is really slow, and this change
> would allow for a performance improvement to still exist on configurations
> that are not necessarily optimized for Core 2.
> 
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> ---

This is a good idea, but warnig it may end up masking broken
hardware. Developers of new drivers will end up never
exercising unaligned DMA, resulting in hardware 
that doesn't work on platforms that have NET_IP_ALIGN set
to 2.

-- 

Re: [net-next-2.6 PATCH] x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN

[H. Peter Anvin]

On 07/01/2010 04:28 PM, Jeff Kirsher wrote:
> From: Alexander Duyck <alexander.h.duyck@intel.com>
> 
> This patch removes the CONFIG_MCORE2 check from around NET_IP_ALIGN.  It is
> based on a suggestion from Andi Kleen.  The assumption is that there are
> not any x86 cores where unaligned access is really slow, and this change
> would allow for a performance improvement to still exist on configurations
> that are not necessarily optimized for Core 2.
> 
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

Acked-by: H. Peter Anvin <hpa@zytor.com>

	-hpa

Re: [net-next-2.6 PATCH] x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN

[David Miller]

From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Date: Thu, 01 Jul 2010 16:28:27 -0700

> From: Alexander Duyck <alexander.h.duyck@intel.com>
> 
> This patch removes the CONFIG_MCORE2 check from around NET_IP_ALIGN.  It is
> based on a suggestion from Andi Kleen.  The assumption is that there are
> not any x86 cores where unaligned access is really slow, and this change
> would allow for a performance improvement to still exist on configurations
> that are not necessarily optimized for Core 2.
> 
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

Applied, with HPA's ack.