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Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-*

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Thank you for contributing to the discussion. I agree that the page I 
cited lacks a lot (I mentioned it), but unfortunately that's the best 
one I could find that touches the subject. Naturally a benchmark would 
be ideal, but again unfortunately I don't have the resources to do one 
myself now. From a pure technical POV, I think that the current choice 
-- a kernel tuned up for desktop use -- is the one that should require a 
benchmark to be adopted, but I get the message.

On 2020-11-22 5:49 p.m., Noah Meyerhans wrote:
> On Sun, Nov 22, 2020 at 03:53:32PM -0800, Flavio Veloso Soares wrote:
>>   Unfortunately, I couldn't find many comprehensive benchmarks of kernel
>>   CONFIG_PREEMPT* options. The one at
>>   [1]https://www.codeblueprint.co.uk/2019/12/23/linux-preemption-latency-throughput.html
>>   seems to be very thorough,
>>
>>   [...]
>>
>>   Not particularly.  I'm used to latency benchmarks showing e.g. average,
>>   90th percentile, 99th percentile, as well as worst.
> I don't think Ben was talking about specific benchmarks.  The web page
> you cites lacks basic measurements one would expect to see from *any*
> meaningful performance benchmark.  Comparing maximum latency is fine,
> but it's not really relevant by itself.  If a configuration change
> improves the worst case (100th percentile) but negatively impacts the
> 50th percentile, is that a change worth making?  Maybe.  But without
> having that data at all, the benchmark really isn't worth much at all.
>
> It's totally reasonable for us to consider making this change, but we
> should have comprehensive data about the impact of doing so.  What
> impact does the change have on different classes of workloads?  e.g.
> high tps, CPU-bound, IO-bound, etc.  It's entirely possible that the
> proposed change improves performance under certain workloads, but
> negatively impacts others.  Without knowing the impact in more in more
> detail, which would allow us to evaluate the tradeoffs, I don't think
> there's a compelling reason to make a change.
>
> noah
>
-- 
FVS

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Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Flavio Veloso <flaviovs@magnux.com> - 2020-10-22 23:30 +0200
  Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Ben Hutchings <ben@decadent.org.uk> - 2020-10-24 03:10 +0200
    Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Flavio Veloso Soares <flaviovs@magnux.com> - 2020-11-22 23:30 +0100
      Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Ben Hutchings <ben@decadent.org.uk> - 2020-11-22 23:40 +0100
        Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Flavio Veloso Soares <flaviovs@magnux.com> - 2020-11-23 01:00 +0100
          Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Noah Meyerhans <noahm@debian.org> - 2020-11-23 03:00 +0100
            Bug#972709: Wishlist/RFC: Change to CONFIG_PREEMPT_NONE in linux-image-cloud-* Flavio Veloso Soares <flaviovs@magnux.com> - 2020-11-25 09:20 +0100

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