linux-kernel - [PATCH v5 0/5] Track and expose idle PURR and SPURR ticks

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Date:   Tue,  7 Apr 2020 14:17:38 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Subject: [PATCH v5 0/5] Track and expose idle PURR and SPURR ticks

From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>

Hi,

This is the fifth version of the patches to track and expose idle PURR
and SPURR ticks. These patches are required by tools such as lparstat
to compute system utilization for capacity planning purposes.

The previous versions can be found here:
v4: https://lkml.org/lkml/2020/3/27/323
v3: https://lkml.org/lkml/2020/3/11/331
v2: https://lkml.org/lkml/2020/2/21/21
v1: https://lore.kernel.org/patchwork/cover/1159341/

They changes from v4 are:

   - As suggested by Naveen, moved the functions read_this_idle_purr()
     and read_this_idle_spurr() from Patch 2 and Patch 3 respectively
     to Patch 4 where it is invoked.

   - Dropped Patch 6 which cached the values of purr, spurr,
     idle_purr, idle_spurr in order to minimize the number of IPIs
     sent.

   - Updated the dates for the idle_purr, idle_spurr in the
     Documentation Patch 5.

Motivation:
===========
On PSeries LPARs, the data centers planners desire a more accurate
view of system utilization per resource such as CPU to plan the system
capacity requirements better. Such accuracy can be obtained by reading
PURR/SPURR registers for CPU resource utilization.

Tools such as lparstat which are used to compute the utilization need
to know [S]PURR ticks when the cpu was busy or idle. The [S]PURR
counters are already exposed through sysfs.  We already account for
PURR ticks when we go to idle so that we can update the VPA area. This
patchset extends support to account for SPURR ticks when idle, and
expose both via per-cpu sysfs files.

These patches are required for enhancement to the lparstat utility
that compute the CPU utilization based on PURR and SPURR which can be
found here :
https://groups.google.com/forum/#!topic/powerpc-utils-devel/fYRo69xO9r4


With the patches, when lparstat is run on a LPAR running CPU-Hogs,
=========================================================================
sudo ./src/lparstat -E 1 3

System Configuration
type=Dedicated mode=Capped smt=8 lcpu=2 mem=4834112 kB cpus=0 ent=2.00 

---Actual---                 -Normalized-
%busy  %idle   Frequency     %busy  %idle
------ ------  ------------- ------ ------
1  99.99   0.00  3.35GHz[111%] 110.99   0.00
2 100.00   0.00  3.35GHz[111%] 111.01   0.00
3 100.00   0.00  3.35GHz[111%] 111.00   0.00

With patches, when lparstat is run on and idle LPAR
=========================================================================
System Configuration
type=Dedicated mode=Capped smt=8 lcpu=2 mem=4834112 kB cpus=0 ent=2.00 
---Actual---                 -Normalized-
%busy  %idle   Frequency     %busy  %idle
------ ------  ------------- ------ ------
1   0.15  99.84  2.17GHz[ 72%]   0.11  71.89
2   0.24  99.76  2.11GHz[ 70%]   0.18  69.82
3   0.24  99.75  2.11GHz[ 70%]   0.18  69.81

Gautham R. Shenoy (5):
  powerpc: Move idle_loop_prolog()/epilog() functions to header file
  powerpc/idle: Store PURR snapshot in a per-cpu global variable
  powerpc/pseries: Account for SPURR ticks on idle CPUs
  powerpc/sysfs: Show idle_purr and idle_spurr for every CPU
  Documentation: Document sysfs interfaces purr, spurr, idle_purr,
    idle_spurr

 Documentation/ABI/testing/sysfs-devices-system-cpu | 39 +++++++++
 arch/powerpc/include/asm/idle.h                    | 93 ++++++++++++++++++++++
 arch/powerpc/kernel/sysfs.c                        | 82 ++++++++++++++++++-
 arch/powerpc/platforms/pseries/setup.c             |  8 +-
 drivers/cpuidle/cpuidle-pseries.c                  | 39 ++-------
 5 files changed, 224 insertions(+), 37 deletions(-)
 create mode 100644 arch/powerpc/include/asm/idle.h

-- 
1.9.4