Possibly, though I have results from a benchmark I've written indicating
the reordering happens at the sender. I believe I found it was due to
the QP striping trick I use to get more bandwidth -- if you back down to
one QP (there's a define in the code you can change), the reordering
rate drops.
Also I do not make any recursive calls to progress -- at least not
directly in the BTL; I can't speak for the upper layers. The reason I
do many completions at once is that it is a big help in turning around
receive buffers, making it harder to run out of buffers and drop frags.
I want to say there was some performance benefit as well but I can't
say for sure.
Andrew
Gleb Natapov wrote:
On Tue, Dec 11, 2007 at 08:03:52AM -0800, Andrew Friedley wrote:
Try UD, frags are reordered at a very high rate so should be a good test.
Good Idea I'll try this. BTW I thing the reason for such a high rate of
reordering in UD is that it polls for MCA_BTL_UD_NUM_WC completions
(500) and process them one by one and if progress function is called
recursively next 500 completion will be reordered versus previous
completions (reordering happens on a receiver, not sender).
Andrew
Richard Graham wrote:
Gleb,
I would suggest that before this is checked in this be tested on a system
that has N-way network parallelism, where N is as large as you can find.
This is a key bit of code for MPI correctness, and out-of-order operations
will break it, so you want to maximize the chance for such operations.
Rich
On 12/11/07 10:54 AM, "Gleb Natapov" <gl...@voltaire.com> wrote:
Hi,
I did a rewrite of matching code in OB1. I made it much simpler and 2
times smaller (which is good, less code - less bugs). I also got rid
of huge macros - very helpful if you need to debug something. There
is no performance degradation, actually I even see very small performance
improvement. I ran MTT with this patch and the result is the same as on
trunk. I would like to commit this to the trunk. The patch is attached
for everybody to try.
--
Gleb.
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