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--></style><title>RE: [openib-general] ip over ib
throughtput</title></head><body>
<div>Have you done any "load" analysis of a 2K .vs. 4K MTU ?
Your analogy of having 2G as a total message size is potentially
flawed. You seem to assume that 2G is the end-all in size, it is not.
What about when you want to (down the road) use IB for files in the
1-10TB in size. Granted, we can live with 2G, but it is not some
nirvana number. Second, with the 2G limit on messages sizes, only
determines the upper bound in overall size, I could send 2G @ 32bytes
MTU. So, the question is, how much less of a system load/impact would
a 4K MTU be over a 2K MTU. Remember, even Ethernet finally decided to
go to Jumbo Frames, why, system impact and more. Remember HIPPI/GSN,
the MTU was 64K, reason, system impact. The numbers I have seen
running IPoIB really impact the system.</div>
<div><br></div>
<div>Steve...</div>
<div><br></div>
<div>At 10:38 AM -0800 1/5/05, Diego Crupnicoff wrote:</div>
<blockquote type="cite" cite><font size="-1">Note however that the
relevant IB limit is the max ***message size*** which happens to be
equal to the ***IB*** MTU for the current IPoIB (that runs on top of
IB UD transport service where IB messages are limited to a single
packet).</font><br>
</blockquote>
<blockquote type="cite" cite><font size="-1">A connected mode IPoIB
(that runs on top of IB RC/UC transport service) would allow IB
messages up to 2GB long. That will allow for much larger (effectively
as large as you may ever dream of) ***IP*** MTUs, regardless of the
underlying IB MTU.</font><br>
</blockquote>
<blockquote type="cite" cite><font size="-1">Diego</font><br>
</blockquote>
<blockquote type="cite" cite><font size="-1">> -----Original
Message-----</font><br>
<font size="-1">> From: Hal Rosenstock [</font><a
href="mailto:halr@voltaire.com"><font
size="-1">mailto:halr@voltaire.com</font></a><font
size="-1">]</font><br>
<font size="-1">> Sent: Wednesday, January 05, 2005 2:21
PM</font><br>
<font size="-1">> To: Peter Buckingham</font><br>
<font size="-1">> Cc: openib-general@openib.org</font><br>
<font size="-1">> Subject: Re: [openib-general] ip over ib
throughtput</font><br>
<font size="-1">></font><br>
<font size="-1">></font><br>
<font size="-1">> On Wed, 2005-01-05 at 12:23, Peter Buckingham
wrote:</font><br>
<font size="-1">> > stupid question: why are we limited to a 2K
MTU for IPoIB?</font><br>
<font size="-1">></font><br>
<font size="-1">> The IB max MTU is 4K. The current HCAs support a
max MTU of 2K.</font><br>
<font size="-1">></font><br>
<font size="-1">> -- Hal</font><br>
<font size="-1">></font><br>
<font size="-1">>
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</blockquote>
<blockquote type="cite" cite><br>
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