[openib-general][patch review] srp: fmr implementation,

[Tom Tucker]

On Wed, 2006-05-10 at 08:36 -0700, Vu Pham wrote:
> Roland Dreier wrote:
> > BTW, does Mellanox (or anyone else) have any numbers showing that
> > using FMRs makes any difference in performance on a semi-realistic benchmark?
> > 
> 
> I'm using xdd to test the performance 
> www.ioperformance.com/products.htm
> 
> The target is Mellanox srp target reference implemenation 
> with 14 SATA spindles
> 
> I can get ~780 MB/s max without FMRs and ~920 MB/s with FMRs 
> (using 256 KB sequential read direct IO request)

Wow, that's awesome Vu! 

So what's the consensus on the reason for the improvement? 
- Fewer WR to send the same amount of data because the memory is
virtually contiguous?
- Fewer PDU due to larger writes and better packing?
- Something else?

Are these huge reads, ... or even better ... what are the parameters to
xdd?

Did you quantify the FMR registration cost per MB of registered memory
space? This would be a very good number to have for figuring out where
the sweet spot is...

Thanks,
Tom T.
> 
> Vu
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