linux-kernel - [PATCH 0/4 v2] x86,cpufreq: unify APERF/MPERF computation

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Date:   Fri, 23 Jun 2017 22:11:50 -0700
From:   Len Brown <lenb@...nel.org>
To:     rafael@...nel.org, tglx@...utronix.de
Cc:     x86@...nel.org, srinivas.pandruvada@...ux.intel.com,
        peterz@...radead.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 0/4 v2] x86,cpufreq: unify APERF/MPERF computation

Hi Rafael, Thomas,

Please see the updated 2nd patch in this series -- in response to tglx review.
Patch 1,3,4 are unchanged.

thanks,
-Len

This patch series has 3 goals:

1. Make "cpu MHz" in /proc/cpuinfo supportable.

2. Make /sys/.../cpufreq/scaling_cur_freq meaningful
   and consistent on modern x86 systems.

3. Use 1. and 2. to remove scheduler and cpufreq overhead

There are 3 main changes since this series was proposed
about a year ago:

This update responds to distro feedback to make /proc/cpuinfo
"cpu MHz" constant.  Originally, we had proposed making it return
the same dynamic value as cpufreq sysfs.

Some community members suggested that sysfs MHz values should
be meaninful, even down to 10ms intervals.  So this has been
changed, versus the original proposal to not re-compute
at intervals shorter than 100ms.

(For those who really care about observing frequency, the
 recommendation remains to use turbostat(8) or equivalent utility,
 which can reliably measure concurrent intervals of arbitrary length)

The intel_pstate sampling mechanism has changed.
Originally this series removed an intel_pstate timer in HWP mode.
Now it removes the analogous scheduler call-back.

Most recently, in response to posting this patch on the list
about 10-days ago, the patch to remove frequency calculation
from inside intel_pstate was dropped, in order to maintain compatibility
with tracing scripts.  Also, the order of the last two patches
has been exchanged.

Please let me know if you see any issues with this series.

thanks!
Len Brown, Intel Open Source Technology Center

The following changes since commit 3c2993b8c6143d8a5793746a54eba8f86f95240f:

  Linux 4.12-rc4 (2017-06-04 16:47:43 -0700)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux.git x86

for you to fetch changes up to 68516d288d3968fe22d6c8984a7bcbdcdbed351d:

  intel_pstate: skip scheduler hook when in "performance" mode. (2017-06-23 22:01:46 -0700)

----------------------------------------------------------------
Len Brown (4):
      x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"
      x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF
      intel_pstate: delete scheduler hook in HWP mode
      intel_pstate: skip scheduler hook when in "performance" mode.

 arch/x86/kernel/cpu/Makefile     |  1 +
 arch/x86/kernel/cpu/aperfmperf.c | 79 ++++++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/proc.c       | 10 +----
 drivers/cpufreq/cpufreq.c        | 12 +++++-
 drivers/cpufreq/intel_pstate.c   | 18 +++------
 include/linux/cpufreq.h          |  2 +
 6 files changed, 100 insertions(+), 22 deletions(-)
 create mode 100644 arch/x86/kernel/cpu/aperfmperf.c