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Subject: Re: [OMPI users] Infiniband performance Problem and stalling
From: Yevgeny Kliteynik (kliteyn_at_[hidden])
Date: 2012-09-02 08:54:35


Randolph,

Some clarification on the setup:

"Melanox III HCA 10G cards" - are those ConnectX 3 cards configured to Ethernet?
That is, when you're using openib BTL, you mean RoCE, right?

Also, have you had a chance to try some newer OMPI release?
Any 1.6.x would do.

-- YK

On 8/31/2012 10:53 AM, Randolph Pullen wrote:
> (reposted with consolidatedinformation)
> I have a test rig comprising 2 i7 systems 8GB RAM with Melanox III HCA 10G cards
> running Centos 5.7 Kernel 2.6.18-274
> Open MPI 1.4.3
> MLNX_OFED_LINUX-1.5.3-1.0.0.2 (OFED-1.5.3-1.0.0.2):
> On a Cisco 24 pt switch
> Normal performance is:
> $ mpirun --mca btl openib,self -n 2 -hostfile mpi.hosts PingPong
> results in:
> Max rate = 958.388867 MB/sec Min latency = 4.529953 usec
> and:
> $ mpirun --mca btl tcp,self -n 2 -hostfile mpi.hosts PingPong
> Max rate = 653.547293 MB/sec Min latency = 19.550323 usec
> NetPipeMPI results show a max of 7.4 Gb/s at 8388605 bytes which seems fine.
> log_num_mtt =20 and log_mtts_per_seg params =2
> My application exchanges about a gig of data between the processes with 2 sender and 2 consumer processes on each node with 1 additional controller process on the starting node.
> The program splits the data into 64K blocks and uses non blocking sends and receives with busy/sleep loops to monitor progress until completion.
> Each process owns a single buffer for these 64K blocks.
> My problem is I see better performance under IPoIB then I do on native IB (RDMA_CM).
> My understanding is that IPoIB is limited to about 1G/s so I am at a loss to know why it is faster.
> These 2 configurations are equivelant (about 8-10 seconds per cycle)
> mpirun --mca btl_openib_flags 2 --mca mpi_leave_pinned 1 --mca btl tcp,self -H vh2,vh1 -np 9 --bycore prog
> mpirun --mca btl_openib_flags 3 --mca mpi_leave_pinned 1 --mca btl tcp,self -H vh2,vh1 -np 9 --bycore prog
> And this one produces similar run times but seems to degrade with repeated cycles:
> mpirun --mca btl_openib_eager_limit 64 --mca mpi_leave_pinned 1 --mca btl openib,self -H vh2,vh1 -np 9 --bycore prog
> Other btl_openib_flags settings result in much lower performance.
> Changing the first of the above configs to use openIB results in a 21 second run time at best. Sometimes it takes up to 5 minutes.
> In all cases, OpenIB runs in twice the time it takes TCP,except if I push the small message max to 64K and force short messages. Then the openib times are the same as TCP and no faster.
> With openib:
> - Repeated cycles during a single run seem to slow down with each cycle
> (usually by about 10 seconds).
> - On occasions it seems to stall indefinitely, waiting on a single receive.
> I'm still at a loss as to why. I can’t find any errors logged during the runs.
> Any ideas appreciated.
> Thanks in advance,
> Randolph
>
>
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