[ofa-general] [PATCH] IB/mlx4: Use pgprot_writecombine() for BlueFlame pages

[Roland Dreier]

 > > with/without CONFIG_X86_PAT gives the same results... 

 > I noted that I have CONFIG_MTRR=y so maybe this can explain the nice latency
 > even without setting X86_PAT?

I don't understand: your results below don't seem to have good results
without X86_PAT?  In any case I don't see how you can get the lowest
latency (from WC mapping to userspace) without X86_PAT, since
pgprot_writecombine() will fall back to pgprot_noncached() is X86_PAT=n.

Anyway, thanks a lot for testing, I'll go ahead and include the patch in
my next pull request.

 > 2.6.29 without CONFIG_X86_PAT 
 > Latency typical: 1.43087 usec
 > Latency best   : 1.41287 usec
 > 
 > 2.6.29 + CONFIG_X86_PAT 
 > Latency typical: 1.43245 usec
 > Latency best   : 1.41295 usec
 > 
 > 2.6.29 + CONFIG_X86_PAT + your patch
 > Latency typical: 1.14896 usec
 > Latency best   : 1.12646 usec
 > 
 > 2.6.29 + CONFIG_X86_PAT + ofed's patch
 > Latency typical: 1.14746 usec
 > Latency best   : 1.12646 usec