Query : Difference between D2H BIDIR vs H2D BIDIR

[alokprasad]

what is difference between D2H BIDIR , vs H2D BIDIR , arent they same and the result should be similar rather asymmetric ( which we see in our setup)

[esitaridi]

@alokprasad they are mirror-image tests:

• H2D BIDIR: measures CPU → GPU bandwidth while a concurrent GPU → CPU transfer interferes.
• D2H BIDIR: measures GPU → CPU bandwidth while a concurrent CPU → GPU transfer interferes.

So both drive traffic in both directions simultaneously, but they time different streams. The result is per-direction throughput, not the H2D+D2H aggregate. nvbandwidth README. Asymmetry is quite plausible on some systems. What is the system you have ?

Could you share the results for:

./nvbandwidth -t host_to_device_memcpy_ce
./nvbandwidth -t device_to_host_memcpy_ce
./nvbandwidth -t host_to_device_bidirectional_memcpy_ce
./nvbandwidth -t device_to_host_bidirectional_memcpy_ce
nvidia-smi topo -m