(Apologies if this was already asked -- this forum doesn't seem to show up as an option when on the "Search Forums" page)
Is Turbo Boost enabled on the MTL machines and if so, how might it affect our speedup measurements, if at all?
Yes, Turbo Boost is enabled on the MTL machines.
For example; the Intel Xeon X7560,is a2.26GHz chip that supports Turbo Boost to overclock the processor when one or more cores aren't needed. Thus if you are running with less that all the cores of a particular chip, then Turbo Boost may be enabled to boost some cores.
I am also looking for more information on Turbo Boost technology. The issue with having turbo boost ON is that if we try to see how our application scales with increasing number of cores, the results might not be as expected.
For instance, the results for an application, I experimented with on MTL, are shown in the figure below. As it can be seen from the figure the performance is super-linear for up to 10 cores and then it is little less than perfectly linear.
If I am not wrong, there is no way to predict that upto x number of cores the frequency is fx and then it steps down to fx' similar to what AMD does. I believe Intel has its own valid reasons but it hinders to gain a clear understanding of what is going on in there. For instance, it can not be predicted if the application is not scaling or it is the processors or something else all together. If there is a way to have one of the batch servers to not have TB it will help.
Thanks for the info, Mike.
My concern (which Dinesh shares) is that Turbo Boost can make speedup analysis inaccurate because it makes an independent variable (i.e., frequency) fluctuate nondeterministically.
I've read that Turbo Boost can be disabled. Is this a possibility on the MTL machines? If so, would you consider doing so?
A related question would be: given the mission of the MTL, what benefit might Turbo Boost provide?
Thanks again for helping run the MTL. It really is a great resource and you guys keep it running well.
I suspect that Turbo Boost on the MTL does notprovide muchvalue, based in part that many of the submitted workloads are running multi-threaded. In fact it may introduce a level of indetermancywhen runningsuch workloads.
I therefore plan toturn-off Turbo Boost on all of the batch nodes - this needs to be accomplished via a BIOS reboot.
I will update this forum when it has been completed.
Thanks again Mike!
Thank you Mike. This will be much appreciated.
Turbo Boost has now been turned off on all the Batch nodes togther with HyperThreading
The login node continues to haveHyperThreading and Turbo Boost set to: On
Initially I thought of asking to have SpeedStep turned off too, but I decided against it because 1) most of our benchmarks very likely run longer than a couple milliseconds -- which is long enough for the frequency to jump to the max level and 2) the MTL energy bill would increase :)
I mention it just in case someone else can think of a good reason to ask to have SpeedStep turned off.