Subject: Re: [PATCH v5 0/5] Track and expose idle PURR and SPURR ticks

From: Gautham R Shenoy <[email-masked]>
Date: Thu, 23 Apr 2020 15:32:13 +0530

On Mon, Apr 20, 2020 at 03:46:35PM -0700, Tyrel Datwyler wrote:
> On 4/7/20 1:47 AM, Gautham R. Shenoy wrote:
> > From: "Gautham R. Shenoy" <[email-masked]>
> > 
> > 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
> > 
> 
> Reviewed-by: Tyrel Datwyler <[email-masked]>

Thanks for reviewing the patches.

> 
> Any chance this is going to be merged in the near future? There is a patchset to
> update lparstat in the powerpc-utils package to calculate PURR/SPURR cpu
> utilization that I would like to merge, but have been holding off to make sure
> we are synced with this proposed patchset.

Michael, could you please consider this for 5.8 ?

--
Thanks and Regards
gautham.