[RFC PATCH] ARM: l2x0: avoid spinlock for sync op on pl310

[Russell King - ARM Linux]

On Mon, Sep 10, 2012 at 02:45:34PM -0500, Rob Herring wrote:
> From: Rob Herring <rob.herring at calxeda.com>
> 
> The sync op is atomic on the pl310, so a spinlock is not needed. It can
> be a bottleneck for code paths with register accesses, so remove it.
> Removing it gives a 30% improvement to pktgen throughput on highbank.
> 
> A similar spinlock removal was originally done by Catalin Marinas[1], but
> the spinlock part was dropped in the merged version. It is unclear why
> other than it was not a runtime selection. As every readl/writel causes a
> outer_sync, the sync function is likely the most critical.

See:

http://lists.arm.linux.org.uk/lurker/message/20110215.164340.dc0ec480.en.html