On Sat, 2013-08-10 at 21:27 -0700, H. Peter Anvin wrote: > On 08/10/2013 09:17 PM, Mike Galbraith wrote: > >> > >> Do you have any quantification of "munches throughput?" It seems odd > >> that it would be worse than polling for preempt all over the kernel, but > >> perhaps the additional locking is what costs. > > > > I hadn't compared in ages, so made some fresh samples. > > > > Q6600 3.11-rc4 > > > > vmark > > voluntary 169808 155826 154741 1.000 > > preempt 149354 124016 128436 .836 > > > > That should be ~worst case, it hates preemption. > > > > tbench 8 > > voluntary 1027.96 1028.76 1044.60 1.000 > > preempt 929.06 935.01 928.64 .900 > > > > hackbench -l 10000 > > voluntary 23.146 23.124 23.230 1.000 > > preempt 25.065 24.633 24.789 1.071 > > > > kbuild vmlinux > > voluntary 3m44.842s 3m42.975s 3m42.954s 1.000 > > preempt 3m46.141s 3m45.835s 3m45.953s 1.010 > > > > Compute load comparisons are boring 'course. > > > > I presume voluntary is indistinguishable from no preemption at all?
No, all preemption options produce performance deltas. > Either way, that is definitely a reproducible test case, so if someone > is willing to take on optimizing preemption they can use vmark as the > litmus test. It would be really awesome if we genuinely could get the > cost of preemption down to where it just doesn't matter. You have to eat more scheduler cycles, that's what PREEMPT does for a living. Release a lock, wham. -Mike -- 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/
