Re: [Gems-users] SMT in GEMS2.1

[Luke Yen <lyen@xxxxxxxxxxx>]

On Mon, 24 Mar 2008, Xuan Qi wrote:

> Hi everyone,
>
> I am trying to configure SMT in GEMS2.1. I checked mfacet.py and
> GEMS/opal/system/system.C but the code for SMT looks kind of strange
> to me. Please help to correct my understanding. Thanks a lot.
>
> in system.C:
>  "m_numSMTProcs = numProcs / CONFIG_LOGICAL_PER_PHY_PROC;"
>
>  so the number of SMT processor is equal the number of processors
>  initiated by simics over the number of config_logical on each SMT
>  processor. And CONFIG_LOGICAL_PER_PHY_PROC should be at least 2 in
>  order to make use of SMT (2 threads can issue
>  instructions simutaneously), am I right?
    Yes, you are correct.
> Next in system.C
>
>  "ASSERT( (cpuNumber >= 0) && (cpuNumber < system_t::inst->m_numProcs) );
>
>  int32 seq_index = cpuNumber;
>  ASSERT(seq_index >= 0 && seq_index < system_t::inst->m_numSMTProcs);"
>
>  As seq_index is equal to cpuNumber, if numProcs = 4, then seq_index can
>  be 0, 1, 2, 3. But if i set CONFIG_LOGICAL_PER_PHY_PROC = 2, the
>  seq_index can only be 0, 1 to satisfy the second assert. It is kind of
>  conflict, isn't it?
   These asserts are confusing but not incorrect.  Ruby only 
knows about SMT processor numbers, so the cpuNumber passed in should be 
less than numProcs.  In your example cpuNumber and seq_index should only be 0,1 if 
the SMT system is set up properly.
   Luke