Re: [Gems-users] Relation between SIMICS cycle & GEMS cycle

["Min Xu (Hsu)" <xu@xxxxxxxxxxx>]

Did you use Opal or just Ruby only? It matters.

On Wed, 29 Mar 2006 Weihang Jiang wrote :
> Hi,
>   Can anybody help me understand the relation between SIMICS
> cycle and GEMS cycle.
> 
>   SIMICS cycle means the number of cycles SIMICS thinks the
> simulation has lasted, which can be calculated through
> calling SIM_cycle_count() at the beginning and the end of
> one simulation.
>   GEMS cycle is referring to the number of cycles opal/ruby
> has advanced.
> 
>   Understanding the relation between SIMICS cycle and GEMS
> cycle is important for utilizing system level profiling
> tools. For example, vmstat reports both number of events
> (e.g. bi, bo) and relative execution time (e.g. us,sy,id).
> Other profiling tools report absolute execution time.
> 
>   I did a small experiment to testify the relation. I ran
> SIMICS+GEMS with two different cache configurations for
> 10,000,000 GEMS cycles.
>   In experiment 1, using fast cache, 407,808 instructions
> have been executed and the SIMICS cycle number is 1,711,569.
> In experiment 2, using slow cache, 401,245 have been
> executed. However, the SIMICS cycle number is 1,664,671
> (different from exp1).
> 
>    Based on this experiment, my understanding is that,
> SIMICS cycle is not an accurate measurement and those system
> level profiling tools can not be used without care.
> 
>    So, I have 2 questions:
> 
> 1. Is my understanding correct?
> 2. How much effort does it require to let SIMICS cycle have
> more sense(i.e. let SIMICS cycle == GEMS cycle)?
> 
> 
> --
> Weihang Jiang,  UIUC
> 
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