Hi, On Thu, May 21, 2015 at 03:06:23PM +0200, Frederic Weisbecker wrote: > On Thu, May 21, 2015 at 05:57:59AM -0700, Paul E. McKenney wrote:
> > Indeed, NO_HZ_FULL is special purpose. You normally would select > > NO_HZ_FULL_ALL only on a system intended for heavy compute without > > normal-workload distractions or for some real-time systems. For mixed > > workloads, you would build with NO_HZ_FULL (but not NO_HZ_FULL_ALL) and > > use the boot parameters to select which CPUs are to be running the > > specialized portion of the workload. > > > > And you would of course need to lead enough CPUs running normally to > > handle the non-specialized portion of the workload. > > > > This sort of thing has traditionally required specialized kernels, > > so the cool thing here is that we can make Linux do it. Though, as > > you noticed, careful configuration is still required. > > > > Seem reasonable? Yes, thanks, some dots got connected :) > That said if he saw a big performance regression after applying these patches, > then there is likely a problem in the patchset. Well it could be due to that > mode > which loops on full dynticks before resuming to userspace. Indeed when that is > enabled, I expect real throughput issues on workloads doing lots of kernel <-> > userspace roundtrips. We just need to make sure this thing only works when > requested. With this change (& having NO_HZ_FULL_ALL), hackbench was being served only by the boot cpu, while w/o this change, all 8 (this is a quad core HT processor) was being used - observation based on 'top'. Regards Afzal -- 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/
