Messages in this thread | | | Date | Thu, 23 Jun 2011 14:51:07 +0200 | From | Ingo Molnar <> | Subject | Re: [patch 4/4] sched: Distangle worker accounting from rq->lock |
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* Tejun Heo <tj@kernel.org> wrote:
> Hello, Ingo. > > On Thu, Jun 23, 2011 at 12:44 PM, Ingo Molnar <mingo@elte.hu> wrote: > > > > * Tejun Heo <tj@kernel.org> wrote: > > > >> The patch description is simply untrue. It does affect how wq > >> behaves under heavy CPU load. The effect might be perfectly okay > >> but more likely it will result in subtle suboptimal behaviors under > >> certain load situations which would be difficult to characterize > >> and track down. Again, the trade off (mostly killing of > >> ttwu_local) could be okay but you can't get away with just claiming > >> "there's no harm". > > > > Well, either it can be measured or not. If you can suggest a specific > > testing method to Thomas, please do. > > Crafting a test case where the suggested change results in worse > behavior isn't difficult (it ends up waking/creating workers which > it doesn't have to between ttwu and actual execution); however, as > with any micro benchmark, the problem is with assessing whether and > how much it would matter in actual workloads (whatever that means) > and workqueue is used throughout the kernel with widely varying > patterns making drawing conclusion a bit tricky. [...]
Well, please suggest a workload where it *matters* - as i suspect any workload tglx will come up with will have another 90% of workloads that you could suggest: so it's much better if you suggest a testing method.
When someone comes to me with a scheduler change i can give them the workloads that they should double check. See the changelog of this recent commit for example:
c8b281161dfa: sched: Increase SCHED_LOAD_SCALE resolution
So please suggest a testing method.
> [...] Given that, changing the behavior for the worse just for this > cleanup doesn't sound like too sweet a deal. Is there any other > reason to change the behavior (latency, whatever) other than the > ttuw_local ugliness?
Well, the ugliness is one aspect of it, but my main concern is simply testability: any claim of speedup or slowdown ought to be testable, right? I mean, we'd like to drive people towards coming with patches and number like Nikhil Rao did in c8b281161dfa, right?
Thanks,
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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