On 03/11/2013 05:40 PM, Ingo Molnar wrote: > > * Michael Wang <wang...@linux.vnet.ibm.com> wrote: > >> Hi, Ingo >> >> On 03/11/2013 04:21 PM, Ingo Molnar wrote: >> [snip] >>> >>> I have actually written the prctl() approach before, for instrumentation >>> purposes, and it does wonders to system analysis. >> >> The idea sounds great, we could get many new info to implement more >> smart scheduler, that's amazing :) >> >>> >>> Any objections? >> >> Just one concern, may be I have misunderstand you, but will it cause >> trouble if the prctl() was indiscriminately used by some applications, >> will we get fake data? > > It's their problem: overusing it will increase their CPU overhead. The two > boundary worst-cases are that they either call it too frequently or too > rarely: > > - too frequently: it approximates the current cpu-runtime work metric > > - too infrequently: we just ignore it and fall back to a runtime metric > if it does not change. > > It's not like it can be used to get preferential treatment - we don't ever > balance other tasks against these tasks based on work throughput, we try > to maximize this workload's work throughput. > > What could happen is if an app is 'optimized' for a buggy scheduler by > changing the work metric frequency. We offer no guarantee - apps will be > best off (and users will be least annoyed) if apps honestly report their > work metric. > > Instrumentation/stats/profiling will also double check the correctness of > this data: if developers/users start relying on the work metric as a > substitute benchmark number, then app writers will have an additional > incentive to make them correct.
I see, I could not figure out how to wisely using the info currently, but I have the feeling that it will make scheduler very different ;-) May be we could implement the API and get those info ready firstly (along with the new sched-pipe which provide work tick info), then think about the way to use them in scheduler, is there any patches on the way? Regards, Michael Wang > > Thanks, > > Ingo > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
