[ofa-general] Re: [RFH] IPoIB retransmission when sending multiple WR's to device

[Krishna Kumar2]

Hi Roland,

Roland Dreier <rdreier at cisco.com> wrote on 08/02/2007 09:59:23 PM:

>  > On the same topic that I wrote about earlier, I put debugs
>  > in my code to store all skbs in bufferA when enqueing multiple
>  > skbs, and store all skbs to bufferB just before doing post.
>  > During post, I compare the two buffers to make sure that I am
>  > not posting in the wrong order, and that never happens.
>  >
>  > But I am getting a huge amount of retransmissions anyway,
>
> Why do you think the retransmissions are related to things being sent
> out of order?  Is it possible you're just sending much faster and
> overrunning the receiver's queue of posted receives?

I cannot be sure of that. But in regular code too, batching is done
in qdisc_run() in a different sense - it sends out packets *iteratively*.
In this case, I see only 225 retransmission for the entire run of all
tests (while in my code, I see 100,000 or more (I think I gave wrong
number earlier, this is the right one - 200 vs 100,000).

Is there any way to avoid the situation you are talking about ? I am
already setting recv_queue_size=4096 when loading ipoib (so for mthca
too).

Thanks,

- KK