cpu,isa,mem: Adds per-thread wakeup logic

Information
Submitter:	Curtis Dunham
Repository:	gem5
Branch:	default
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Description

Changes wakeup functionality so that only specific threads on SMT
capable cpus are woken.

Testing Done

so what is the difference between

    xc->getCpuPtr()->wakeup(xc->threadId());

and

    xc->activate();

?  I think we need to clarify whether or not these are equivalent, and if so, why we need both, and if not, what the differences are and when you should be using one vs. the other.

Mitch Hayenga Aug. 12, 2015, 12:47 p.m. (Aug. 12, 2015, 12:47 p.m.)

From what I can tell, wakeup does more... Making sure the CPU knows to clock itself, setting the adress monitor to reflect that a wakeup occured, etc. In general wakeup is related to quiesce events (WFI/WFE on ARM). Activate looks to be more just related to setting the thread to be listed as runnable + a few statistics. Wakeup seems to call activate.

Alexandru Dutu Aug. 20, 2015, 11:13 a.m. (Aug. 20, 2015, 11:13 a.m.)

Just looking at the O3 cpu model, FullO3CPU<Impl>::wakeCPU() and FullO3CPU<Impl>::activateContext(ThreadID tid) are equivalent. Even more, it seems that FullO3CPU<Impl>::wakeup() calls both of them and schedules 2 wakeup events instead of one. It might be that I am missing something, though I will expose my understanding in a mere effort to sparkle a discussion which will clarify some hindered aspects. The intent seems to be for wakeCPU to be used whenever there is no particular hardware thread which needs to wakeup (i.e. during a drain) and activateContext when the thread to be activated is known. As far I can tell wakeup seems bogus and should be replaced with activateContext.

src/cpu/kvm/base.hh (Diff revision 1)

having a default value here seems a little sketchy---how many more places are there where there's no explicity thread ID?

Mitch Hayenga Aug. 12, 2015, 12:47 p.m. (Aug. 12, 2015, 12:47 p.m.)

This was done just for the cores, etc that don't support multi-threading currently. Other assertions should trigger if you try to run them with multiple threads.

You have a pending review.

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Status: Closed (submitted)