linux-kernel - Re: Integration of SCST in the mainstream Linux kernel

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Message-ID: <e2e108260802180301o5c376024t72e649a9debd5157@mail.gmail.com>
Date:	Mon, 18 Feb 2008 12:01:27 +0100
From:	"Bart Van Assche" <bart.vanassche@...il.com>
To:	"Erez Zilber" <erezz@...taire.com>
Cc:	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>,
	rdreier@...co.com, James.Bottomley@...senpartnership.com,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	vst@...b.net, linux-scsi@...r.kernel.org,
	scst-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: Integration of SCST in the mainstream Linux kernel

On Feb 18, 2008 10:43 AM, Erez Zilber <erezz@...taire.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.
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