PSM2 is the only valid implementation for OmniPath (OPA).  UCX also
supports OmniPath, but it does so via Verbs, thus getting much lower
performance (typically 3 GiB/s instead of 10 GiB/s).

To work around that, give the mtl_psm2 component a higher priority
than the pml_ucx component.

See <https://www.mail-archive.com/users@lists.open-mpi.org/msg33581.html>.

--- openmpi-4.0.2/ompi/mca/mtl/psm2/mtl_psm2_component.c	2019-11-15 17:06:15.142076840 +0100
+++ openmpi-4.0.2/ompi/mca/mtl/psm2/mtl_psm2_component.c	2019-11-15 17:06:22.242009379 +0100
@@ -126,7 +126,7 @@ ompi_mtl_psm2_component_register(void)
         setenv("PSM2_DEVICES", "self,shm", 0);
     }
 
-    param_priority = 40;
+    param_priority = 55;
     (void) mca_base_component_var_register (&mca_mtl_psm2_component.super.mtl_version,
                                             "priority", "Priority of the PSM2 MTL component",
                                             MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,

Likewise for PSM: we want InfiniPath to be taken care of by PSM, not by UCX,
since UCX achieves worse performance.

--- openmpi-4.0.2/ompi/mca/mtl/psm/mtl_psm_component.c
+++ openmpi-4.0.2/ompi/mca/mtl/psm/mtl_psm_component.c
@@ -92,7 +92,7 @@ ompi_mtl_psm_component_register(void)
 
 
     /* set priority high enough to beat ob1's default */
-    param_priority = 30;
+    param_priority = 54;
     (void) mca_base_component_var_register (&mca_mtl_psm_component.super.mtl_version,
                                             "priority", "Priority of the PSM MTL component",
                                             MCA_BASE_VAR_TYPE_INT, NULL, 0, 0,
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<div class='path'>path: <a href='/guix/log/?id=7b9ee58925406f5d608fca06db5479e16970dc91'>root</a>/<a href='/guix/log/gnu?id=7b9ee58925406f5d608fca06db5479e16970dc91'>gnu</a>/<a href='/guix/log/gnu/system?id=7b9ee58925406f5d608fca06db5479e16970dc91'>system</a>/<a href='/guix/log/gnu/system/uuid.scm?id=7b9ee58925406f5d608fca06db5479e16970dc91'>uuid.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/system/uuid.scm?id=7b9ee58925406f5d608fca06db5479e16970dc91&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-09-23 18:17:17 +0200'>2021-09-23</span></td><td><a href='/guix/commit/gnu/system/uuid.scm?id=90604348e14913da48327da05113d7da8ae7655a'>uuid: Support XFS.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/uuid.scm (string-&gt;xfs-uuid): New procedure.
(%uuid-parsers, %uuid-printers): Add ‘xfs’ file system type.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-11-07 13:40:46 +0100'>2020-11-07</span></td><td><a href='/guix/commit/gnu/system/uuid.scm?id=e87471dc510bc393e3306fba86f919dc6bf89b7b'>uuid: Add support for bcachefs.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/uuid.scm (string-&gt;bcachefs-uuid): New exported procedure.
(%uuid-parsers, %uuid-printers): Add the ‘bcachefs’ file system type.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-26 18:35:10 +0200'>2020-07-26</span></td><td><a href='/guix/commit/gnu/system/uuid.scm?id=675e56221e3dfc58cac94bf30835f16a9c41d530'>file-systems: Add NTFS support.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/uuid.scm (%ntfs-endianness): New macro,
(ntfs-uuid-&gt;string): new procedure,
(%ntfs-endianness): new variable,
(string-&gt;ntfs-uuid): new exported procedure,
(%uuid-parsers): add NTFS support,
(%uuid-printers): add NTFS support.
* gnu/build/file-systems.scm (%ntfs-endianness): New macro,
(ntfs-superblock?, read-ntfs-superblock, ntfs-superblock-uuid,
check-ntfs-file-system): new procedure,
(%partition-uuid-readers): add NTFS support,
(check-file-system): add NTFS support.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-06-18 23:24:37 -0400'>2020-06-18</span></td><td><a href='/guix/commit/gnu/system/uuid.scm?id=04a4af6dd4fbfcfc564eac5eafe647b192ba3a8f'>uuid: Prevent a loop on invalid arguments.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/uuid.scm (uuid=?): Use type predicates in the fallback case to
prevent looping on invalid arguments.
</span></span></td><td>Maxim Cournoyer</td></tr>