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

[Petr Vorel]

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

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