Re: [LTP] [PATCH v2] sched_football: synchronize with kickoff flag to reduce skew

[Petr Vorel <pvorel@suse.cz>]

> Hi all,

> ...
> > Checking the configurations of the stock kernel and the real-time
> > kernel, the stock kernel uses "CONFIG_PREEMPT_VOLUNTARY=y,"
> > which only provides voluntary preemption.

> Yes, CONFIG_PREEMPT_VOLUNTARY=y is in all mainline defconfigs
> (arch/*/configs/*_defconfig). Therefore we have it in our Tumbleweed (6.16.3-1)
> and in upcoming SLES16 (6.12 based). SLE15-SP7 (6.4 based) use
> CONFIG_PREEMPT_NONE=y instead.

> Looking at the history It works well on all archs, we just recently had a
> problem with ppc64le hmc on SLE16 (regular ppc64le works). Later I'll check
> history of older SLES versions.

> And most importantly I'll try to run manually with -i (more stress test).

> > This preemption model is designed to strike a balance between throughput
> > and latency. It only allows the kernel to be preempted at specific, well
> > defined
> > "safe points," potentially resulting in long, unbounded latencies.

> > However, the sched_football test was most likely designed to measure or
> > stress-test the deterministic, low-latency scheduling behavior that is
> > characteristic of real-time (RT) kernel.

> > So, I tend to believe the test's failure on the stock kernel is acceptable.
> > And, by the way, what does the SUSE kernel configuration look like?


> > # grep CONFIG_PREEMPT /boot/config-6.12.0-55.29.1.el10_0.x86_64
> > CONFIG_PREEMPT_BUILD=y
> > CONFIG_PREEMPT_VOLUNTARY=y
> > # CONFIG_PREEMPT is not set
> > # CONFIG_PREEMPT_RT is not set
> > CONFIG_PREEMPT_COUNT=y
> > CONFIG_PREEMPTION=y
> > CONFIG_PREEMPT_DYNAMIC=y
> > CONFIG_PREEMPT_RCU=y
> > CONFIG_PREEMPT_NOTIFIERS=y

> > (^ I built my v6.17-rc4 with this config too)

> /boot/config-6.12.0-160000.4-default # Tumbleweed x68_64
> CONFIG_PREEMPT_BUILD=y
> # CONFIG_PREEMPT_NONE is not set
> CONFIG_PREEMPT_VOLUNTARY=y
> # CONFIG_PREEMPT is not set
> # CONFIG_PREEMPT_LAZY is not set
> # CONFIG_PREEMPT_RT is not set
> CONFIG_PREEMPT_COUNT=y
> CONFIG_PREEMPTION=y
> CONFIG_PREEMPT_DYNAMIC=y
> CONFIG_PREEMPT_RCU=y
> CONFIG_PREEMPT_NOTIFIERS=y
> # CONFIG_PREEMPT_TRACER is not set
> CONFIG_PREEMPTIRQ_DELAY_TEST=m

> Upcoming SLE16 is similar to Tumbleweed.

> /boot/config-6.4.0-150700.714.ga8e7017-default # SLE15-SP7 x86_64 RT
> CONFIG_PREEMPT_BUILD=y
> CONFIG_PREEMPT_NONE=y
> # CONFIG_PREEMPT_VOLUNTARY is not set
> # CONFIG_PREEMPT is not set
> # CONFIG_PREEMPT_RT is not set
> CONFIG_PREEMPT_COUNT=y
> CONFIG_PREEMPTION=y
> CONFIG_PREEMPT_DYNAMIC=y
> CONFIG_PREEMPT_RCU=y
> CONFIG_PREEMPT_NOTIFIERS=y
> # CONFIG_PREEMPT_TRACER is not set
> CONFIG_PREEMPTIRQ_DELAY_TEST=m

> /boot/config-6.4.0-150700.5-rt # SLE15-SP7 x86_64 RT
> CONFIG_PREEMPT_LAZY=y
> # CONFIG_PREEMPT_NONE is not set
> # CONFIG_PREEMPT_VOLUNTARY is not set
> # CONFIG_PREEMPT is not set
> CONFIG_PREEMPT_RT=y
> CONFIG_PREEMPT_COUNT=y
> CONFIG_PREEMPTION=y
> CONFIG_PREEMPT_RCU=y
> CONFIG_PREEMPT_NOTIFIERS=y
> # CONFIG_PREEMPT_TRACER is not set
> CONFIG_PREEMPTIRQ_DELAY_TEST=m

And looking on some other distros, e.g. Debian had CONFIG_PREEMPT_VOLUNTARY=y on
6.12.38+deb13 (from recently released stable Debian 13 trixie), but they changed
it to CONFIG_PREEMPT_LAZY=y in 6.16.3+deb14 (for upcoming Debian forky (testing)
- in devel for now). I would expect that setup for RT kernel.

> Kind regards,
> Petr

> > # grep CONFIG_PREEMPT /boot/config-6.12.0-55.31.1.el10_0.x86_64+rt
> > CONFIG_PREEMPT_BUILD=y
> > CONFIG_PREEMPT=y
> > CONFIG_PREEMPT_RT=y
> > CONFIG_PREEMPT_COUNT=y
> > CONFIG_PREEMPTION=y
> > # CONFIG_PREEMPT_DYNAMIC is not set
> > CONFIG_PREEMPT_RCU=y
> > CONFIG_PREEMPT_NOTIFIERS=y

I suppose this RT kernel has CONFIG_PREEMPT_LAZY=y, right?

Kind regards,
Petr

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