linux-kernel - Re: [PATCH] x86/tsc: Add tsc_tuned_baseclk flag disabling CPUID.16h use for tsc calibration

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 for Android: free password hash cracker in your pocket

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

Message-ID: <pdsz0EbsOFH8qmBn1Uv20EOOr71rKXljZIItC75EhT9KO4TKEKrt83Es88ZeaAh3MYuk0UM8F6XKfvmmRHgZjF50CXk9sigWEH_SyXp6lZE=@protonmail.com>
Date:   Mon, 20 Jan 2020 11:15:24 +0000
From:   Krzysztof Piecuch <piecuch@...tonmail.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "corbet@....net" <corbet@....net>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "mchehab+samsung@...nel.org" <mchehab+samsung@...nel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "pawan.kumar.gupta@...ux.intel.com" 
        <pawan.kumar.gupta@...ux.intel.com>,
        "paulmck@...ux.ibm.com" <paulmck@...ux.ibm.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "drake@...lessm.com" <drake@...lessm.com>,
        "malat@...ian.org" <malat@...ian.org>,
        "mzhivich@...mai.com" <mzhivich@...mai.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/tsc: Add tsc_tuned_baseclk flag disabling CPUID.16h use for tsc calibration

On Friday, January 17, 2020 4:37 PM, Andy Lutomirski <luto@...capital.net> wrote:
> Wouldn’t it be better to have an option tsc_max_refinement= to increase the 1%?

All that is in the commends about it say that:

 * If there are any calibration anomalies (too many SMIs, etc),
 * or the refined calibration is off by 1% of the fast early
 * calibration, we throw out the new calibration and use the
 * early calibration.

I still don't fully understand why the "1% rule" exists.

Ideally it would be better to get the early calibration right than risk getting
it wrong because of an "anomaly".
OTOH if you system doesn't support any of the early calibration methods other
than CPUID.16h (mine doesn't support either PIT or MSR) "tsc_max_refinement"
would allow you to control max tsc_hz error.

If you think that would be better please let me know.