Re: [Linux Kernel 5.13 GA] ESXi Performance regression

[Rahul Gopakumar]

> sysctl_sched_wakeup_granularity's default value hasn't been touched since
> 2009:
> 
> 172e082a9111 ("sched: Re-tune the scheduler latency defaults to decrease worst-case latencies")
>
> and the automagic scaling (see kernel/sched/fair.c::update_sysctl()) hasn't
> changed much either.
> 
> What's likely to happen here is that you have a service in your distro (or
> somesuch) tweaking those values and since the incriminated commit moves
> those files to /sys/kernel/debug/sched/, said service doesn't do anything
> anymore.

Hi Valentin,

In our testing, we use RHEL 8.1 distro. It looks like tuned daemon updates
15ms (per tuned virtual-guest profile) in /proc/sys/kernel/sched_wakeup_granularity_ns
file during tuned's startup.

Now tuned daemon is not able to update the value as the commit moves those
files to debugs and thus sched_wakeup_granularity_ns file remains with the
default value.

Regards,
Rahul Gopakumar,
Performance Engineering,
VMware, Inc.