I agree with Paul on the fact that a FAQ update would be great on this
subject. /dev/shm seems a good place to put the temporary files (when
available, of course).
Putting files in /dev/shm also showed better performance on our systems,
even with /tmp on a local disk.
Sylvain
On Sun, 16 May 2010, Paul H. Hargrove wrote:
If I google "ompi sm btl performance" the top match is
http://www.open-mpi.org/faq/?category=sm
I scanned the entire page from top to bottom and don't see any questions of
the form
Why is SM performance slower than ...?
The words "NFS", "network", "file system" or "filesystem" appear nowhere on
the page. The closest I could find is
7. Where is the file that sm will mmap in?
The file will be in the OMPI session directory, which is typically
something like /tmp/openmpi-sessions-myusername@mynodename* . The file
itself will have the name shared_mem_pool.mynodename. For example, the full
path could be
/tmp/openmpi-sessions-myusername@node0_0/1543/1/shared_mem_pool.node0.
To place the session directory in a non-default location, use the MCA
parameter orte_tmpdir_base.
which says nothing about where one should or should not place the session
directory.
Not having read the entire FAQ from start to end, I will not contradict
Ralph's claim that the "your SM performance might suck if you put the session
directory on a remote filesystem" FAQ entry does exist, but I will assert
that I did not find it in the SM section of the FAQ. I tried google on "ompi
session directory" and "ompi orte_tmpdir_base" and still didn't find whatever
entry Ralph is talking about. So, I think the average user with no clue
about the relationship between the SM BLT and the session directory would
need some help finding it. Therefore, I still feel an FAQ entry in the SM
category is warranted, even if it just references whatever entry Ralph is
referring to.
-Paul
Ralph Castain wrote:
We have had a FAQ on this for a long time...problem is, nobody reads it :-/
Glad you found the problem!
On May 14, 2010, at 3:15 PM, Paul H. Hargrove wrote:
Oskar Enoksson wrote:
Christopher Samuel wrote:
Subject: Re: [OMPI devel] Very poor performance with btl sm on twin
nehalem servers with Mellanox ConnectX installed
To: de...@open-mpi.org
Message-ID:
<d45958078cd65c429557b4c5f492b6a60770e...@is-ex-bev3.unimelb.edu.au>
Content-Type: text/plain; charset="iso-8859-1"
On 13/05/10 20:56, Oskar Enoksson wrote:
The problem is that I get very bad performance unless I
explicitly exclude the "sm" btl and I can't figure out why.
Recently someone reported issues which were traced back to
the fact that the files that sm uses for mmap() were in a
/tmp which was NFS mounted; changing the location where their
files were kept to another directory with the orte_tmpdir_base
MCA parameter fixed that issue for them.
Could it be similar for yourself ?
cheers,
Chris
That was exactly right, as you guessed these are diskless nodes that
mounts the root filesystem over NFS.
Setting orte_tmpdir_base to /dev/shm and btl_sm_num_fifos=9 and then
running mpi_stress on eight cores measures speeds of 1650MB/s for both
1MB messages and 1600MB/s for 10kB messages.
Thanks!
/Oskar
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Sounds like a new FAQ entry is warranted.
-Paul
--
Paul H. Hargrove phhargr...@lbl.gov
Future Technologies Group
HPC Research Department Tel: +1-510-495-2352
Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
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--
Paul H. Hargrove phhargr...@lbl.gov
Future Technologies Group Tel: +1-510-495-2352
HPC Research Department Fax: +1-510-486-6900
Lawrence Berkeley National Laboratory
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