Re: [PATCH 2/3] x86_64: Define 128-bit memory-mapped I/O operations

On Wed, 2012-08-22 at 10:30 -0400, Benjamin LaHaise wrote:

On Wed, Aug 22, 2012 at 03:24:59PM +0100, Ben Hutchings wrote:

quoted

-#ifdef EFX_USE_QWORD_IO
+#if defined(EFX_USE_OWORD_IO)
+       _efx_writeo(efx, value->u128, reg);
+#elif defined(EFX_USE_QWORD_IO)
        _efx_writeq(efx, value->u64[0], reg + 0);
        _efx_writeq(efx, value->u64[1], reg + 8);
 #else

This looks like a perfect fit for write combining.  I have traces showing 
that enabling write combining on MMIO does indeed generate a single PCIe 
transaction on at least a couple of different current systems.  Why is 
that not an option?

Because reordering, and see the comment at the top of this file.

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.