RE: [PATCH] x86: intel_epb: Add earlyparam option to keep bias at performance

David Woodhouse
2023-12-05T12:00:45Z

Paul writes:
> The problem is that this will take effect even on a kexec and hence it is throttling
> a system that set ENERGY_PERF_BIAS_PERFORMANCE prior to the kexec. We use kexec to
> live update the host kernel of our systems whilst leaving virtual machines running.
> This resetting of the perf bias is having a very detrimental effect on the downtime
> of our systems across the live update - about a 7 fold increase.

It isn't just about kexec, is it? Even in a clean boot why wouldn't we want to stay in performance mode until the kernel has *finished* booting? It's literally adding seconds to the startup time in some cases.

And yes, we *particularly* care in the kexec case because guests experience it as excessive steal time. But it ain't great in the general case either, surely?