[openib-general] some questions: sdp/perftest/hyperthreading

[umaxx]

Hello,

I have a couple of questions after playing around with OpenIB these
days, hope you can help me.

1. from userspace/libsdp/src/port.c:

    ...
      printf("default libsdp configuration is used\n");
#define LIBSDP_DEFAULT_CONFIG_FILE  "/usr/local/ibgd/etc/libsdp.conf"
    __sdp_read_config(LIBSDP_DEFAULT_CONFIG_FILE);
    ...

Why is LIBSDP_DEFAULT_CONFIG_FILE pointing to this location?
Shouldn't this be something more useful like $sysconf?
And maybe you can add a note to README / or a comment to 
libsdp.conf - that it is possible to set the environment 
variable LIBSDP_CONFIG_FILE?

2. Is it better to test performance with disabled Hyperthreading?
perftest/rdma_lat is using get_cycles(). get_cycles() uses internal
the rdtscll() function. Correct me if I am wrong, but this could be a 
problem with a hyperthreading enabled cpu? Because it's not clear which 
cpu(-core) is used by rdtsll() at which time? The time stamp counters 
between processors are not synchronized, and therefore the timing 
measured will be incorrect.
Maybe something like cpuid() is missing - to set/get the wanted?

3. In the SDP-slide
(http://openib.org/docs/oib_wkshp_082205/das_SDP_Linux.pdf) from the
workshop is a measurement with perftest on a Dual-Xeon with enabled HT
done. Was there SMP-Support enabled in the kernel? 

Regards,

Joerg Zinke