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Message-ID: <e2e108260802051102y1b02bcdic5ea9c45caee9964@mail.gmail.com>
Date: Tue, 5 Feb 2008 20:02:06 +0100
From: "Bart Van Assche" <bart.vanassche@gmail.com>
To: "Erez Zilber" <erezz@voltaire.com>
Subject: Re: Integration of SCST in the mainstream Linux kernel
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Vladislav Bolkhovitin" <vst@vlnb.net>,
       James.Bottomley@hansenpartnership.com,
       "FUJITA Tomonori" <fujita.tomonori@lab.ntt.co.jp>,
       linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net,
       linux-kernel@vger.kernel.org
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On Feb 5, 2008 6:10 PM, Erez Zilber <erezz@voltaire.com> wrote:
> One may claim that STGT should have lower performance than SCST because
> its data path is from userspace. However, your results show that for
> non-IB transports, they both show the same numbers. Furthermore, with IB
> there shouldn't be any additional difference between the 2 targets
> because data transfer from userspace is as efficient as data transfer
> from kernel space.
>
> The only explanation that I see is that fine tuning for iSCSI & iSER is
> required. As was already mentioned in this thread, with SDR you can get
> ~900 MB/sec with iSER (on STGT).

My most recent measurements also show that one can get 900 MB/s with
STGT + iSER on an SDR IB network, but only for very large block sizes
(>= 100 MB). A quote from Linus Torvalds is relevant here (February 5,
2008):

    Block transfer sizes over about 64kB are totally irrelevant for
99% of all people.

Please read my e-mail (posted earlier today) with a comparison for 4
KB - 64 KB block transfer sizes between SCST and STGT.

Bart Van Assche.
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