Re: [Gems-users] Change in cpu frequency - question

[Pradeep Ramachandran <pramach2@xxxxxxxx>]

On Feb 7, 2010, at 10:52 AM, Dan Gibson wrote:

> The ways of Simics are strange indeed. I have no idea why 75MHz  
> would be blazing fast but 80MHz would be slow. You might try asking  
> on the Simics forum about it.
Thanks Dan. I have posted it on simics.net. I can update this group  
with what they say once they respond.
> There is a higher-level point to consider. Bear in mind with the  
> following comment that I have no idea what you're actually trying to  
> simulate.
I am trying to do fault injections when running simics+gems. I don't  
need to model timing and such with a high degree of accuracy, but it  
is important that I functionally simulate all operations of the  
workload with a reasonable degree of accuracy.
> I would advise against simulating a workload that is actually  
> performing I/O when you are taking measurements -- Simics' I/O  
> timing isn't sufficiently realistic, and GEMS does nothing to  
> improve I/O timing from what Simics provides. Instead, set up your  
> workload so that its "I/O operations" are consistently hitting in  
> memory -- either in the file cache or in a loopback device. In other  
> words, make sure you have fully warmed your input sets from disk,  
> and that you're not actually hitting any ethernet devices. Doing so  
> creates a decent proxy for a server busy period, without spending  
> CPU time just spinning in the idle loop (after all, its hard to  
> convince reviewers that optimizing the idle loop is interesting).
But if I am simulating a server workload in a distributed client- 
server setting, wouldn't I want to make sure that I am having network  
communication (that is simulated by simics) in my measurement window?
Pradeep.