I propose that when there is no MTU in the partition policy file OpenSM use a configurable default from: /etc/cache/opensm/opensm.opt. Something like: # The default MTU to be used for IPoIB and other MCGs when the partition-policy # does not provide exact value. The default is the lowest possible MTU mcg_default_mtu 1 Eitan Zahavi Senior Engineering Director, Software Architect Mellanox Technologies LTD Tel:+972-4-9097208 Fax:+972-4-9593245 P.O. Box 586 Yokneam 20692 ISRAEL
________________________________
From: Shirley Ma [mailto:[EMAIL PROTECTED]
Sent: Wednesday, July 25, 2007 10:45 PM
To: Eitan Zahavi
Cc: [email protected]; Hal Rosenstock
Subject: RE: [ofa-general] Re: openSM: Different IB MTUs
Hello Eitan, Hal,
Thanks. It's good openSM has the configuration option to set up
these attributes in MC. Is this a good idea to add below to openSM: When
there is no MTU defined in the configuration file, SM can pick up the
smallest link MTU in the fabrics by default? MTU is unlikely rate,
slower rate might indicate the cablling problem. So using the smallest
link MTU in the fabrics might not be a bad choice for MC by default. The
reason I request here is to create IP multicast group, MTU is not an
attribute of the group. When mapping IP multicast to IB multicast, IB
muliticast might fail because of different IB link MTU size in the
group, but IP multicast group will be successful without knowing the
failure. If admin sets MTU in configuration file, admin would know this
failure. Otherwise, admin/users could spend too much time on debugging
their broken multicasting applications.
Thanks
Shirley Ma
"Eitan Zahavi" <[EMAIL PROTECTED]>
"Eitan Zahavi" <[EMAIL PROTECTED]>
07/25/07 12:25 PM
To
"Hal Rosenstock" <[EMAIL PROTECTED]>, Shirley
Ma/Beaverton/[EMAIL PROTECTED]
cc
<[email protected]>
Subject
RE: [ofa-general] Re: openSM: Different IB MTUs
Hi Shirley,
I think I understand where your question comes from...
Many have issue with heterogonous fabrics where not all nodes
have same MTU or Speed.
Especially when IPoIB relies on all nodes joining the broadcast
group.
The term "join" for multicast groups is a little overloaded.
If a node joins an existing MC group it has to have a rate
(speed * width) > MCG.rate and support MTU > MCG.MTU otherwise it is
denied.
If the join is actually a "create" the node has to provide the
rate and MTU which define the MCG values.
To allow for administrator to control the IPoIB MCGs MTU and
rate OpenSM provides the means to control these
values per partition. See the doc/partition-config.doc
Still the administrator should know what would be the lowest MTU
and rate the nodes expected to join the IPoIB subnet have.
The tradeoff is in the hands of the administrator who can set a
value that will prevent slow nodes from joining the group,
or assign a low value that will fit all nodes but slow down
communication ...
EZ
Eitan Zahavi
Senior Engineering Director, Software Architect
Mellanox Technologies LTD
Tel:+972-4-9097208
Fax:+972-4-9593245
P.O. Box 586 Yokneam 20692 ISRAEL
________________________________
From: [EMAIL PROTECTED] [
mailto:[EMAIL PROTECTED] On Behalf Of Hal
Rosenstock
Sent: Wednesday, July 25, 2007 10:01 PM
To: Shirley Ma
Cc: [email protected]
Subject: [ofa-general] Re: openSM: Different IB MTUs
Shirley,
On 7/25/07, Shirley Ma <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> >
wrote:
Hal,
Thanks for your prompt reply. I am asking for how openSM
handle different link MTUs in SA MCMemberRecord MTU. For example, if we
have some links MTU as 2K, some links MTU as 1K. Then when enabling
IPoIB, how does SM decide IPoIB broadcast group MCMemberRecord MTU size?
When creating an IB multicast group from a 2K MTU node first, which PMTU
value is attaching to this IB multicast group MCMemberRecord MTU?
MCMemberRecord MTU gets the group MTU (when created). This is
either this first joiner with sufficient components or preconfigured
(and MTU can be set in the config). If a joiner has insufficient MTU for
the group, it is denied.
-- Hal
Thanks
Shirley Ma
"Hal Rosenstock" < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> >
"Hal Rosenstock" <
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> >
07/25/07 10:57 AM
To
Shirley Ma/Beaverton/[EMAIL PROTECTED]
cc
[email protected] <mailto:[email protected]>
Subject
Re: openSM: Different IB MTUs
Shirley,
On 7/25/07, Shirley Ma < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> > wrote:
Hello Hal,
How does openSM handle CAs with
different MTUs in the same subnet? For example, IPoIB broadcast group
MTU, IB multicast group PMTU? Does openSM pick up the smallest MTU in
the subnet?
Are you asking about link MTU, SA
PathRecord/MultiPathRecord MTU, SA MCMemberRecord MTU, or all of these ?
-- Hal
Thanks
Shirley Ma
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