Re: [PATCH 0/3] x86_64, sfc: 128-bit memory-mapped I/O

On Tue, 2012-08-21 at 18:38 -0700, H. Peter Anvin wrote:

On 08/21/2012 06:17 PM, Ben Hutchings wrote:

quoted

Current Solarflare network controllers have 128-bit memory-mapped
registers which are normally accessed through a series of I/O
operations.  However, it is also possible to access them with a single
MOVAPS instruction on x86_64, and this is measurably faster as it
requires only one PCIe transaction.

Also, have you considered doing this with write combining instead?

We tried it, and it goes horribly wrong.  On some systems, the writes
are not combined, but they are reordered in a way the hardware doesn't
support.  See the comment at the top of drivers/net/ethernet/sfc/io.h.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.