[PATCH] ARM: lib: use LDRD/STRD for data copy

Russell King - ARM Linux linux at arm.linux.org.uk
Mon Mar 19 11:41:23 EDT 2012

On Mon, Mar 19, 2012 at 09:36:41AM -0500, Rob Herring wrote:
> On 03/19/2012 03:55 AM, Russell King - ARM Linux wrote:
> > On Mon, Mar 19, 2012 at 04:02:48PM +0900, Boojin Kim wrote:
> >> This patch uses LDRD/STRD that loads and stores data as DWORD unit
> >> for the copy of 8-words data.
> >> It brings better performance than LDRM/STRM that was used originally.
> > 
> > And what about CPUs that don't have ldrd/strd ?
> > 
> And what about CPUs that do have ldrd/strd but is slower than ldm/stm?
> I'm pretty sure that is almost everything currently out there.

The double-word load/stores were introduced in ARMv6.  Some Intel based
CPUs prior to this have the support as well.  Everything else doesn't.

So taht's nowhere close to 'almost everything'.

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