Messages in this thread | | | Date | Wed, 29 Jun 2005 16:54:22 -0700 | From | "Paul E. McKenney" <> | Subject | Re: PREEMPT_RT and I-PIPE: the numbers, take 3 |
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On Wed, Jun 29, 2005 at 03:57:34PM -0700, Bill Huey wrote: > On Wed, Jun 29, 2005 at 06:29:24PM -0400, Kristian Benoit wrote: > > Overall analysis: > ... > > We had not intended to redo a 3rd run so early, but we're happy we did > > given the doubts expressed by some on the LKML. And as we suspected, these > > new results very much corroborate what we had found earlier. As such, our > > conclusions remain mostly unchanged: > > Did you compile your host Linux kernel with CONFIG_SMP in place ? That's > critical since a UP kernel removes both spinlock and blocking locks in > critical paths makes micro benchmarks sort of invalid. > > The benchmark is sort of confusing two things and merging them into one. > Both the latency statistic and kernel performance must be kept seperate. > The overall kernel performance is a more complicate issue that has to be > analysize differently using a more complicated methodology. That because > an RTOS use of PREEMPT_RT is going to be under a different circumstance > than that of a pure dual kernel set up of some sort. The functionalities > aren't the same. > > I suggest that you compile the dual kernel with SMP turned on and try it > again, otherwise it's not really testing the overhead of any of the locking > for either the PREEMPT_RT or dual kernel set ups. That's really the only > outstanding statistic that I've noticed in that benchmark.
If you were suggesting this to be run on an SMP system, I would agree with you. I, too, would very much like to see these results run on a 2-CPU or 4-CPU system, although I am most certainly -not- asking Kristian and Karim to do this work -- it is very much someone else's turn in the barrel, I would say!
However, on a UP system, I have to agree with Kristian's choice of configuration. An embedded system developer running on a UP system would naturally use a UP Linux kernel build, so it makes sense to benchmark a UP kernel on a UP system.
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