On 15 February 2013 20:40, Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote: > Hi Vincent, > > On 02/15/2013 06:58 PM, Vincent Guittot wrote: >> Hi Srivatsa, >> >> I have run some tests with you branch (thanks Paul for the git tree) >> and you will find results below. >> > > Thank you very much for testing this patchset! > >> The tests condition are: >> - 5 CPUs system in 2 clusters >> - The test plugs/unplugs CPU2 and it increases the system load each 20 >> plug/unplug sequence with either more cyclictests threads >> - The test is done with all CPUs online and with only CPU0 and CPU2 >> >> The main conclusion is that there is no differences with and without >> your patches with my stress tests. I'm not sure that it was the >> expected results but the cpu_down is already quite low : 4-5ms in >> average >> > > Atleast my patchset doesn't perform _worse_ than mainline, with respect > to cpu_down duration :-) yes exactly and it has pass more than 400 consecutive plug/unplug on an ARM platform > > So, here is the analysis: > Stop-machine() doesn't really slow down CPU-down operation, if the rest > of the CPUs are mostly running in userspace all the time. Because, the > CPUs running userspace workloads cooperate very eagerly with the stop-machine > dance - they receive the resched IPI, and allow the per-cpu cpu-stopper > thread to monopolize the CPU, almost immediately. > > The scenario where stop-machine() takes longer to take effect is when > most of the online CPUs are running in kernelspace, because, then the > probability that they call preempt_disable() frequently (and hence inhibit > stop-machine) is higher. That's why, in my tests, I ran genload from LTP > which generated a lot of system-time (system-time in 'top' indicates activity > in kernelspace). Hence my patchset showed significant improvement over > mainline in my tests. > ok, I hadn't noticed this important point for the test > However, your test is very useful too, if we measure a different parameter: > the latency impact on the workloads running on the system (cyclic test). > One other important aim of this patchset is to make hotplug as less intrusive > as possible, for other workloads running on the system. So if you measure > the cyclictest numbers, I would expect my patchset to show better numbers > than mainline, when you do cpu-hotplug in parallel (same test that you did). > Mainline would run stop-machine and hence interrupt the cyclic test tasks > too often. My patchset wouldn't do that, and hence cyclic test should > ideally show better numbers. In fact, I haven't looked at the results as i was more interested by the load that was generated > > I'd really appreciate if you could try that out and let me know how it > goes.. :-) Thank you very much! ok, I'm going to try to run a test series Vincent > > Regards, > Srivatsa S. Bhat > >> >> >> On 12 February 2013 04:58, Srivatsa S. Bhat >> <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote: >>> On 02/12/2013 12:38 AM, Paul E. McKenney wrote: >>>> On Mon, Feb 11, 2013 at 05:53:41PM +0530, Srivatsa S. Bhat wrote: >>>>> On 02/11/2013 05:28 PM, Vincent Guittot wrote: >>>>>> On 8 February 2013 19:09, Srivatsa S. Bhat >>>>>> <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote: >>>> >>>> [ . . . ] >>>> >>>>>>> Adding Vincent to CC, who had previously evaluated the performance and >>>>>>> latency implications of CPU hotplug on ARM platforms, IIRC. >>>>>>> >>>>>> >>>>>> Hi Srivatsa, >>>>>> >>>>>> I can try to run some of our stress tests on your patches. >>>>> >>>>> Great! >>>>> >>>>>> Have you >>>>>> got a git tree that i can pull ? >>>>>> >>>>> >>>>> Unfortunately, no, none at the moment.. :-( >>>> >>>> You do need to create an externally visible git tree. >>> >>> Ok, I'll do that soon. >>> >>>> In the meantime, >>>> I have added your series at rcu/bhat.2013.01.21a on -rcu: >>>> >>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git >>>> >>>> This should appear soon on a kernel.org mirror near you. ;-) >>>> >>> >>> Thank you very much, Paul! :-) >>> >>> Regards, >>> Srivatsa S. Bhat >>> > > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
