On Fri, Jul 15, 2011 at 02:10:21AM +0200, Lennert Buytenhek wrote:

On Thu, Jul 07, 2011 at 01:38:25PM +0100, Russell King - ARM Linux wrote:

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I suppose for the majority of the cases, the overhead of the indirect
function call is near-zero, compared to the overhead of the cache
management operation, so it would only make a difference for coherent
systems without an IOMMU. Do we care about micro-optimizing those?

FWIW, when I was hacking on ARM access point routing performance some
time ago, turning the L1/L2 cache maintenance operations into inline
functions (inlined into the ethernet driver) gave me a significant and
measurable performance boost.

On what architecture?  Can you show what you did to gain that?

Patch is attached below.  It's an ugly product-specific hack, not
suitable for upstreaming in this form, etc etc, but IIRC it gave me
a ~5% improvement on packet routing.

Do you know how much is contributed from each change - L1, L2, moving
dma_cache_maint() inline, removing the virt_addr_valid() etc?