Re: Integration of SCST in the mainstream Linux kernel

Bart Van Assche
2008-02-18T11:01:41Z

On Feb 18, 2008 10:43 AM, Erez Zilber <erezz@voltaire.com> wrote:
> If you use a high value for FirstBurstLength, all (or most) of your data
> will be sent as unsolicited data-out PDUs. These PDUs don't use the RDMA
> engine, so you miss the advantage of IB.

Hello Erez,

Did you notice the e-mail Roland Dreier wrote on Februari 6, 2008 ?
This is what Roland wrote:
> I think the confusion here is caused by a slight misuse of the term
> "RDMA". It is true that all data is always transported over an
> InfiniBand connection when iSER is used, but not all such transfers
> are one-sided RDMA operations; some data can be transferred using
> send/receive operations.

Or: data sent during the first burst is not transferred via one-sided
remote memory reads or writes but via two-sided send/receive
operations. At least on my setup, these operations are as fast as
one-sided remote memory reads or writes. As an example, I obtained the
following numbers on my setup (SDR 4x network);
ib_write_bw: 933 MB/s.
ib_read_bw: 905 MB/s.
ib_send_bw: 931 MB/s.

Bart Van Assche.