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

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Date:   Tue, 5 Dec 2023 10:23:02 +0000
From:   Jack Allister <jalliste@...zon.com>
To:     <dave.hansen@...el.com>
CC:     <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
        <hdegoede@...hat.com>, <hpa@...or.com>, <jalliste@...zon.com>,
        <juew@...zon.com>, <len.brown@...el.com>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <pdurrant@...zon.com>, <peterz@...radead.org>,
        <rafael.j.wysocki@...el.com>, <rafael@...nel.org>,
        <tglx@...utronix.de>, <usama.arif@...edance.com>, <x86@...nel.org>
Subject: Re: [PATCH] x86: intel_epb: Add earlyparam option to keep bias at performance

> This is fundamentally a hack.

I do not totally agree that this is a hack, the setting of it to the
ENERGY_PERF_BIAS_NORMAL is an equivalent workaround which is used for
systems where the platform firmware has not configured it as expected
for laptops etc. and that is already present.

> It sounds like you want the system default to be at
> ENERGY_PERF_BIAS_PERFORMANCE.  You also mentioned that this was done "on
> kernel boot".  How did you do that, exactly?  Shouldn't that "on kernel
> boot" action be reflected over here rather than introducing another
> command-line parameter?

As Paul has mentioned, we perform live-updates of the host kernel running
on servers. This is done while virtual machines are still running so that
there is no perceived downtime for the guest/customer. This requires a
kexec into the new kernel and there are specific areas such as PCI device
enumeration which can take a substantial amount of time in it's current
form and can be perceived as downtime while the kernel is loading.

> Shouldn't that "on kernel
> boot" action be reflected over here rather than introducing another
> command-line parameter?

A kernel parameter may not be the most elegant solution, would a proposal
for a kernel build configuration be a bit more suitable?