[mvapich-discuss] MCAST feature

[Hoang-Vu Dang]

Hi Hari,

Thanks for the quick response, 
When I try to enable mcast (it’s not by default), it’s slower in some cases.. 
Is there anything else to tune ? is it using mcast when messages are larger ?

Below is without(default) and with mcast

+ srun -n 8 ./osu/osu_bcast

# OSU MPI Broadcast Latency Test v5.3.2
# Size       Avg Latency(us)
1                       2.14
2                       2.12
4                       2.11
8                       2.22
16                      2.22
32                      2.45
64                      2.51
128                     2.59
256                     2.75
512                     2.81
1024                    3.06
2048                    3.56
4096                    4.82
8192                    7.19
16384                   9.17
32768                  13.27
65536                  21.18
131072                 36.82
262144                 67.67
524288                128.95
1048576               200.37

+ export MV2_USE_MCAST=1
+ MV2_USE_MCAST=1
+ srun -n 8 ./osu/osu_bcast

# OSU MPI Broadcast Latency Test v5.3.2
# Size       Avg Latency(us)
1                       1.59
2                       1.53
4                       1.57
8                       1.65
16                      1.65
32                      1.67
64                      1.66
128                     1.73
256                     2.07
512                     2.15
1024                    2.42
2048                    3.08
4096                    3.95
8192                    5.54
16384                   8.13
32768                  13.74
65536                  25.09
131072                 54.59
262144                103.71
524288                206.69
1048576               414.35

> On Jul 23, 2017, at 3:16 PM, Hari Subramoni <subramoni.1 at osu.edu> wrote:
> 
> Hi Vu,
> 
> Yes - this support is still available in MVAPICH2. It is enabled by default at configure time if the system has the necessary driver level support (i.e. IB umad libraries). You can enable it at runtime using environment variables.
> 
> Please refer to the following section of the user guide for more information
> 
> http://mvapich.cse.ohio-state.edu/static/media/mvapich/mvapich2-2.3a-userguide.html#x1-660006.8 <http://mvapich.cse.ohio-state.edu/static/media/mvapich/mvapich2-2.3a-userguide.html#x1-660006.8>
> 
> Please let us know if you run into any issues with it.
> 
> Thx,
> Hari.
> 
> On Sun, Jul 23, 2017 at 4:12 PM, Hoang-Vu Dang <dang.hvu at gmail.com <mailto:dang.hvu at gmail.com>> wrote:
> Hi,
> 
> I would like to test the hardware multicast feature of Inifniband. Is it still available inside MVAPICH2 ? If yes, is there any relevant environment variable ? anything to look for ?
> 
> For example: how to enable/disable, threshold for performance tuning ? If I choose RC, is the mode available etc..
> 
> Thanks,
> Vu
> 
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