linux-kernel - Re: [PATCH] arm64: Provide an AMU-based version of arch_freq_get_on

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: <20230607095856.7nyv7vzuehceudnl@bogus>
Date:   Wed, 7 Jun 2023 10:58:56 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Beata Michalska <beata.michalska@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        mark.rutland@....com, will@...nel.org, rafael@...nel.org,
        viresh.kumar@...aro.org, ionela.voinescu@....com,
        sumitg@...dia.com, Sudeep Holla <sudeep.holla@....com>,
        yang@...amperecomputing.com
Subject: Re: [PATCH] arm64: Provide an AMU-based version of
 arch_freq_get_on_cpu

On Tue, Jun 06, 2023 at 04:57:54PM +0100, Beata Michalska wrote:
> With the Frequency Invariance Engine (FIE) being already wired up with
> sched tick and making use of relevant (core counter and constant
> counter) AMU counters, getting the current frequency for a given CPU
> on supported platforms, can be achieved by utilizing the frequency scale
> factor which reflects an average CPU frequency for the last tick period
> length.
> 
> With that at hand, arch_freq_get_on_cpu dedicated implementation
> gets enrolled into cpuinfo_cur_freq policy sysfs attribute handler,
> which is expected to represent the current frequency of a given CPU,
> as obtained by the hardware. This is exactly the type of feedback that
> cycle counters provide.
> 
> In order to avoid calling arch_freq_get_on_cpu from the scaling_cur_freq
> attribute handler for platforms that do provide cpuinfo_cur_freq, and
> yet keeping things intact for those platform that do not, its use gets
> conditioned on the presence of cpufreq_driver (*get) callback (which also
> seems to be the case for creating cpuinfo_cur_freq attribute).
>

LGTM,

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

However I fail to understand if both the changes are dependent ?
Can this be split into 2 patches ? I fail to see the dependency, what
am I missing ? Even if there is some dependency to get arch value
(arch_freq_get_on_cpu() from show_cpuinfo_cur_freq()), you can push
that change first followed by the arm64 change as 2 different change.

-- 
Regards,
Sudeep