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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5322CF05-344D-4ADE-B38C-7DCE7F076E0C@infradead.org>
Date:   Tue, 05 Dec 2023 12:15:48 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     pdurrant@...zon.co.uk, bp@...en8.de, dave.hansen@...el.com,
        dave.hansen@...ux.intel.com, hdegoede@...hat.com, hpa@...or.com,
        jalliste@...zon.co.uk, juew@...zon.com, len.brown@...el.com,
        linux-kernel@...r.kernel.org, mingo@...hat.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

On 5 December 2023 12:12:09 GMT, "Rafael J. Wysocki" <rafael@...nel.org> wrote:
>On Tue, Dec 5, 2023 at 1:00 PM David Woodhouse <dwmw2@...radead.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.