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

David Woodhouse
2023-12-05T12:16:21Z

On 5 December 2023 12:12:09 GMT, "Rafael J. Wysocki" <rafael@kernel.org> wrote:
>On Tue, Dec 5, 2023 at 1:00 PM David Woodhouse <dwmw2@infradead.org> wrote:
>>
>>
>> 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?
>
>Because it may overheat during that period.
>
>> 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?
>
>So IMV it would be perfectly fine to add a command line arg to provide
>the initial value of energy_perf_bias for the ones who know what they
>are doing.

We don't even care about setting it to an "initial value" during boot. We just want to leave it how it was already set up.