On Jun 9, 2010, at 11:57 AM, Jeff Squyres wrote:
> This, of course, begs the question of whether we should use sysv
> shmem or not. It seems like the order of preference should be:
> - sysv
> - mmap in a tmpfs
> - mmap in a "regular" (but not networked) fs
> The big downer, of course, is the whole "what happens if the job
> crashes?" issue. With mmap, an rm -rf will clean up any leftover
> files (although looking for them in /dev/shm might be a bit non-
> obvious). With sysv, you have to use the ipc* commands to look for
> and whack any orphan shmem segments.
System V shared memory cleanup is a concern only if a process dies in
between shmat and shmctl IPC_RMID. Shared memory segment cleanup
should happen automagically in most cases, including abnormal process
Samuel K. Gutierrez
Los Alamos National Laboratory
> Right now, the orted/hnp won't clean up any left over sysv
> segments. This seems like something we should fix.
> But even with that, if the orted/hnp is killed, sysv segments can
> get let over. Hrm.
> On Jun 9, 2010, at 11:58 AM, Sylvain Jeaugey wrote:
>> As stated at the conf call, I did some performance testing on a 32
>> So, here is graph showing 500 timings of an allreduce operation
>> 15,000 times for good timing) with sysv, mmap on /dev/shm and mmap on
>> What is shows :
>> - sysv has the better performance ;
>> - having the mmap file in /dev/shm is very close to sysv. We only
>> +0.1 us for a complete allreduce operation, but it seems stable.
>> The noise
>> is identical to sysv (must be OS noise) ;
>> - having the mmap file in /tmp (ext3) decreases performance (+0.4 us
>> compared to /dev/shm) and seems prone to some "other" noise.
>> Warning : the graph does not start at 0.
>> On Tue, 27 Apr 2010, Samuel K. Gutierrez wrote:
>>> With Jeff and Ralph's help, I have completed a System V shared
>>> component for Open MPI. I have conducted some preliminary tests
>>> on our
>>> systems, but would like to get test results from a broader audience.
>>> As it stands, mmap is the defaul, but System V shared memory can
>>> be activated
>>> using: -mca mpi_common_sm sysv
>>> Input is greatly appreciated!
>>> Samuel K. Gutierrez
>>> Los Alamos National Laboratory
>>> devel mailing list
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> Jeff Squyres
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