[openib-general] [PATCH][3/7]ipoib performance patches -- remove tx_ring

[Shirley Ma]

Roland Dreier <rdreier at cisco.com> wrote on 05/25/2006 04:28:27 PM:

>     Shirley> didn't help somehow.  Even in some code, I induced some
>     Shirley> locks, the overall performance of all these 7 patches I
>     Shirley> am trying to post here could improve IPoIB from 20% - 80%
>     Shirley> unidirectional and doubled bidirectional.
> 
> I'm guessing that all of that gain comes from letting the send and
> receive completion handlers run simultaneously.  Is that right?
> 
> For example how much of an improvement do you see if you just apply
> the patches you've posted -- that is, only 1/7, 2/7 and 3/7?
> 
>  - R.

That's not true. I tested performance with 1/7, 3/7 a couple weeks ago, I 
saw more than 10% improvement. I never saw send queue overrun with tx_ring 
before on one cpu with one TCP stream. After removing tx_ring, the send 
path is much faster, the default 128 is not bigger enough to handle it. 
That's the reason I have another patch to handler send queue overrun -- 
requeue the packet to the head of dev xmit queue instead of current 
implementation which is silently dropped the packets when device driver 
send queue is full, and depends on TCP retransmission. This implementation 
would cause TCP fast trans, slow start, and packets out of orders.

Thanks
Shirley Ma
IBM Linux Technology Center
15300 SW Koll Parkway
Beaverton, OR 97006-6063
Phone(Fax): (503) 578-7638


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