OpenBMC kernel and CONFIG_PREEMPT

[William Kennington]

It's interesting because I think it has a bigger impact on the 8xx chip
than the 7xx chip. AFAIK I was indirectly comparing this and it seems like
it didn't make a huge difference for us on our older BMCs. We have it
disabled on our 5.15 configs, but used it in 5.10. I don't think we noticed
a meaningful difference when porting forward. Probably you need a certain
amount of startup services trying to steal time from each other.

On Fri, Apr 7, 2023 at 12:10 PM Patrick Williams <patrick at stwcx.xyz> wrote:

> Joel,
>
> Would you mind looking at this commit[1]?  Nuvoton seems to have a lot
> of data that suggests that disabling CONFIG_PREEMPT leads to
> significantly better performance.  The boot time is almost 50% faster.
>
> I'm surprised that:
>
>     1. CONFIG_PREEMPT really results in that worse of performance.
>     2. The Nuvoton chip is special from any other ARM variant in this
>        regard.
>
> Should we disable this across the board on all our platforms?
>
> 1.
> https://github.com/openbmc/openbmc/commit/52ec37dd0b8776ce7f43e65e0be578c3606340b7
> --
> Patrick Williams
>
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