[openib-general] Re: PATCH] mthca - command interface - revised

[Roland Dreier]

    Michael> AFAIK, which of the two options gives better performance
    Michael> might depend on the application and the specific system.
    Michael> For now, Eli made the simpler option the default.

Have you seen cases where using the HCR is faster?  It seems that in
both cases we are doing posted writes to PCI memory, except that the
HCR case has to do at least one (slow) read to check the go bit.  The
doorbell case does use more write barriers since all the writes have
to be ordered, but I have a hard time believing that the write
barriers are anywhere near as expensive as the read of the go bit.

 - R.