From: Magdalena Dobosz <maj.dobosz@gmail.com>
To: CPUFREQ@vger.kernel.org
Cc: Ross Lagerwall <rosslagerwall@gmail.com>,
rjw@rjwysocki.net, viresh.kumar@linaro.org
Subject: cpufreq-info and acpi-cpufreq: reporting MSR_IA32_PERF_CTL as "actual frequency"
Date: Tue, 25 Nov 2014 18:21:12 +0100 [thread overview]
Message-ID: <CAHOOexvOXKr4s-mg20VdUOAR3o7EN5iAS-ModAk6-vNKbhwT=g@mail.gmail.com> (raw)
Hi,
I was analyzing the code and behaviour of cpufrequtils (kernel 3.13).
I noticed that the value reported by cpufreq-info as the frequency
"asserted by call to hardware" (exported to sysfs as
"cpuinfo_cur_freq") is always the same as the value reported as the
frequency requested by a governor (exported to sysfs as "freq", stored
in policy->cur).
It was not the case for kernel 3.2 (these two values tend to differ).
I found a reason: while using acpi-cpufreq driver, the value reported
as hardware frequency is retrieved using get_cur_freq_on_cpu function
(defined in acpi-cpufreq). Now, in kernel version 3.2 this function
reads a value from MSR_IA32_PERF_STATUS, while in kernel 3.13 it reads
MSR_IA32_PERF_CTL.
It is a result of the patch shown below:
https://lists.ubuntu.com/archives/kernel-team/2013-June/029493.html
It looks like a bug for me - we take a requested frequency (control
register) and we report it as "cpuinfo_cur_freq - Current frequency of
the CPU as obtained from the hardware, in KHz. This is the frequency
the CPU actually runs at." (as desribed in cpufrequtils documentation:
https://www.kernel.org/doc/Documentation/cpu-freq/user-guide.txt". I
believe we should read status register (MSR_IA32_PERF_STATUS) instead.
Best regards,
Magdalena Dobosz
next reply other threads:[~2014-11-25 17:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-25 17:21 Magdalena Dobosz [this message]
2014-11-26 6:07 ` cpufreq-info and acpi-cpufreq: reporting MSR_IA32_PERF_CTL as "actual frequency" Viresh Kumar
2014-11-26 15:29 ` Dirk Brandewie
2014-11-26 20:41 ` Magdalena Dobosz
2014-11-26 22:37 ` Rafael J. Wysocki
2014-11-27 16:38 ` Magdalena Dobosz
2015-03-14 17:18 ` Len Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAHOOexvOXKr4s-mg20VdUOAR3o7EN5iAS-ModAk6-vNKbhwT=g@mail.gmail.com' \
--to=maj.dobosz@gmail.com \
--cc=CPUFREQ@vger.kernel.org \
--cc=rjw@rjwysocki.net \
--cc=rosslagerwall@gmail.com \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).