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Subject: Re: [OMPI devel] 1.3 PML default choice
From: George Bosilca (bosilca_at_[hidden])
Date: 2009-01-13 20:36:27

That's pretty weird, but you're right. Here is the code that do
exactly what you state.

     } else if(strcmp(ompi_mtl_base_selected_component-
>mtl_version.mca_component_name, "psm") != 0) {
         /* if mtl is not PSM then back down priority, and require the
user to */
         /* specify pml cm directly if that is what they want
priority */
         /* of 1 is sufficient in that case as it is the only pml
that */
         /* will be considered */
         *priority = 1;


On Jan 13, 2009, at 20:31 , Brian Barrett wrote:

> George -
> I don't care what we end up doing, but what you state is wrong. We
> do not use the CM for all other MTLs by default. PSM is the *ONLY*
> MTL that will cause CM to be used by default. Portals still falls
> back to OB1 by default. Again, don't care, don't want to change,
> just want the documentation and current behavior to match.
> Brian
> On Jan 13, 2009, at 6:27 PM, George Bosilca wrote:
>> This topic was raised on the mailing list quite a few times. There
>> is a major difference between the PSM and the MX support. For PSM
>> there is just an MTL, which makes everything a lot simpler. The
>> problem with MX is that we have an MTL and a BTL. In order to
>> figure out which one to use, we have to call the init function and
>> this function initialize MX. The MTL use the default values for
>> this, while the BTL give some hints to the MX library (about how to
>> behave based on the support level we want, i.e. such as who will
>> deal with shared memory or self communications). As there can be
>> only one MX initialization, as the MTL initialize first, the BTL
>> will always get a wrongly initialized MX library (which can
>> generate some performance problems).
>> What Brian describe is the best compromise we manage to find few
>> months ago. If you want to get the MX CM to run, you will have to
>> clearly specify on the command line --mca pml cm. All other MTL
>> will have the behavior described on the README.
>> george.
>> On Jan 13, 2009, at 20:18 , Brian Barrett wrote:
>>> On Jan 13, 2009, at 5:48 PM, Patrick Geoffray wrote:
>>>> Jeff Squyres wrote:
>>>>> Gaah! I specifically asked Patrick and George about this and
>>>>> they said that the README text was fine. Grr...
>>>> When I looked at that time, I vaguely remember that _both_ PMLs
>>>> were initialized but CM was eventually used because it was the
>>>> last one. It looked broken, but it worked in the end (MTL was
>>>> used with CM PML). I don't know if that behavior changed since.
>>> I just tested 1.3rc4 with MX and it uses the btl by default. The
>>> reason is the cm init lowers the priority to 1 unless the MTL that
>>> loaded is psm, in which case it stays at the higher default of
>>> 30. It's a fairly easy fix, I think. But the last time this was
>>> discussed people in the group had objections to using the MTL by
>>> default with MX.
>>> Brian
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