On 9/14/07, Alexander Kolbasov <[EMAIL PROTECTED]> wrote: > During any particular clock cycle do you consider a core to be busy if > there is an instruction active? Yes
>Is it busier if there are four > instructions active instead of one? No, the IPC of a workload is a characteristic of that workload, all the OS can do is give clock cycles to a workload >Is it equally busy whether the > instruction is in an execution unit, waiting on per-core cache, waiting > on per-chip cache, or waiting on memory? Yes, but it would be nice to know if its waiting on some level of the memory hierarchy > Is it any busier if it has both > an integer and a floating point instruction active? For shared FPU Niagara this is an issue, not an issue for most CPUs By the time it could be addressed in software, will anyone still care about Niagara? >What if it's > handling instructions for a scout thread, is that active or inactive? Inactive, if its just prefetching loads, active if its executing instructions > If > there's one FP unit per 8 cores and it's active, which core gets to > count that as active? They all do, just like blocking on any shared resource. > If some functional units may be dynamically > reconfigured then is a core which owns such a unit and isn't using it > any less busy than one which does not own such a unit? No, but Intel hyperthreading and Power6 style reconfigurable pipelines vary the work done per clock cycle independently of the application workload, so not all clock ticks have the same value. > > Just being Devil's advocate. I don't doubt that you should be able to > improve the measurement significantly. I just think that the notion of > CPU utilization is a vague and processor dependent concept, and you > shouldn't expect to get any perfect answers. I agree. I think that things that are largely deterministic for a given workload (pipeline utilization) can be ignored in the OS level metrics, there are other tools for getting at these effects. Things that are non-deterministic (mostly sharing/coupling effects between workloads) need to be instrumented, because they are the main cause of surprises and problems. Adrian > > "Everyone just needs to give 110 percent." > University of Connecticut basketball coach Jim Calhoun > > > ------- End of Forwarded Message > > > > _______________________________________________ > perf-discuss mailing list > perf-discuss@opensolaris.org > _______________________________________________ perf-discuss mailing list perf-discuss@opensolaris.org
