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

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Message-Id: <1586250289.bjlqf3xvt0.naveen@linux.ibm.com>
Date:   Tue, 07 Apr 2020 14:35:22 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v5 0/5] Track and expose idle PURR and SPURR ticks

Gautham R. Shenoy wrote:
> 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

Thanks, LGTM. For the series:
Acked-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>


- Naveen