On 02/08/2013 10:14 PM, Srivatsa S. Bhat wrote: > On 02/08/2013 09:11 PM, Russell King - ARM Linux wrote: >> On Thu, Feb 07, 2013 at 11:41:34AM +0530, Srivatsa S. Bhat wrote: >>> On 02/07/2013 09:44 AM, Rusty Russell wrote: >>>> "Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> writes: >>>>> On 01/22/2013 01:03 PM, Srivatsa S. Bhat wrote: >>>>> Avg. latency of 1 CPU offline (ms) [stop-cpu/stop-m/c latency] >>>>> >>>>> # online CPUs Mainline (with stop-m/c) This patchset (no stop-m/c) >>>>> >>>>> 8 17.04 7.73 >>>>> >>>>> 16 18.05 6.44 >>>>> >>>>> 32 17.31 7.39 >>>>> >>>>> 64 32.40 9.28 >>>>> >>>>> 128 98.23 7.35 >>>> >>>> Nice! >>> >>> Thank you :-) >>> >>>> I wonder how the ARM guys feel with their quad-cpu systems... >>>> >>> >>> That would be definitely interesting to know :-) >> >> That depends what exactly you'd like tested (and how) and whether you'd >> like it to be a test-chip based quad core, or an OMAP dual-core SoC. >> > > The effect of stop_machine() doesn't really depend on the CPU architecture > used underneath or the platform. It depends only on the _number_ of > _logical_ CPUs used. > > And stop_machine() has 2 noticeable drawbacks: > 1. It makes the hotplug operation itself slow > 2. and it causes disruptions to the workloads running on the other > CPUs by hijacking the entire machine for significant amounts of time. > > In my experiments (mentioned above), I tried to measure how my patchset > improves (reduces) the duration of hotplug (CPU offline) itself. Which is > also slightly indicative of the impact it has on the rest of the system. > > But what would be nice to test, is a setup where the workloads running on > the rest of the system are latency-sensitive, and measure the impact of > CPU offline on them, with this patchset applied. That would tell us how > far is this useful in making CPU hotplug less disruptive on the system. > > Of course, it would be nice to also see whether we observe any reduction > in hotplug duration itself (point 1 above) on ARM platforms with lot > of CPUs. [This could potentially speed up suspend/resume, which is used > rather heavily on ARM platforms]. > > The benefits from this patchset over mainline (both in terms of points > 1 and 2 above) is expected to increase, with increasing number of CPUs in > the system. > Adding Vincent to CC, who had previously evaluated the performance and latency implications of CPU hotplug on ARM platforms, IIRC. 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
