[focal:linux][PATCH 0/1] LP:#1756311 -

[Marcelo Henrique Cerri]

On Thu, Apr 08, 2021 at 01:07:54AM +0100, Colin Ian King wrote:
> On 08/04/2021 00:50, Marcelo Henrique Cerri wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1756311
> 
> Is thus the correct buglink?
> 
> > 
> > 
> > [Impact]
> > 
> > The CONFIG_NO_HZ_FULL=y Kconfig option causes the kernel to avoid
> > sending scheduling-clock interrupts to CPUs with a single runnable
> > task, and such CPUs are said to be "adaptive-ticks CPUs". This is
> > important for applications with aggressive real-time response
> > constraints because it allows them to improve their worst-case
> > response times by the maximum duration of a scheduling-clock
> > interrupt. It is also important for computationally intensive
> > short-iteration workloads: If any CPU is delayed during a given
> > iteration, all the other CPUs will be forced to wait idle while the
> > delayed CPU finishes. Thus, the delay is multiplied by one less than
> > the number of CPUs. In these situations, there is again strong
> > motivation to avoid sending scheduling-clock interrupts.
> > 
> > 
> > [Test Plan]
> > 
> > In order to verify the change will not cause performance issues in
> > context switch we should compare the results for:
> > 
> > ./stress-ng --seq 0 --metrics-brief -t 15
> 
> Some of those stress tests will have a lot of jitter and random
> variance. Running tests multiple times for longer durations is best, so
> I've actually got some performance tests already for this kind of
> testing...  the autotest-client-tests that may be better to run are:
> 
> ubuntu_performance_stress_ng
> ubuntu_performance_stream
> ubuntu_performance_latency
> ubuntu_performance_misc
> 
> I can't see the test data but since these changes affect a range of
> architectures were the tests run on all the architectures affected by
> the config changes?

Hi, Colin.

Since it needs to be run on bare metal I only ran them for amd64. I
will check if I can prepare a test kernel on a PPA and maybe run it
through out regression tests.

I'm assuming those autotest tests take care of running stress-ng
multiple times and report the performance results. Is that right?

> 
> > 
> > Running on a dedicated machine and with the following services
> > disabled: smartd.service, iscsid.service, apport.service,
> > cron.service, anacron.timer, apt-daily.timer, apt-daily-upgrade.timer,
> > fstrim.timer, logrotate.timer, motd-news.timer, man-db.timer.
> > 
> > The results didn't show any performance regression:
> > 
> > https://kernel.ubuntu.com/~mhcerri/lp1919154/
> 
> I can't read the data - I don't have read permsssion.

You should be able to access the data via the browser. Let me know if
you can't.

> > 
> > 
> > [Where problems could occur]
> > 
> > Performance degradation might happen for workloads with intensive
> > context switching.
> > 
> > 
> > ---
> > Marcelo Henrique Cerri (1):
> >   UBUNTU: [Config] CONFIG_NO_HZ_FULL=y
> > 
> >  debian.master/config/amd64/config.common.amd64  |  1 +
> >  debian.master/config/annotations                | 17 +++++++++--------
> >  debian.master/config/arm64/config.common.arm64  |  1 +
> >  debian.master/config/armhf/config.common.armhf  |  1 +
> >  debian.master/config/config.common.ubuntu       |  9 ++++++---
> >  debian.master/config/i386/config.common.i386    |  1 +
> >  .../config/ppc64el/config.common.ppc64el        |  2 +-
> >  debian.master/config/s390x/config.common.s390x  |  2 +-
> >  8 files changed, 21 insertions(+), 13 deletions(-)
> > 
> 
> 
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-- 
Regards,
Marcelo