linux-kernel - Re: [RFC] Display the cpu of sched domain in procfs

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Date:   Wed, 19 Feb 2020 09:53:44 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Valentin Schneider <valentin.schneider@....com>,
        Chen Yu <yu.chen.surf@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Mel Gorman <mgorman@...e.de>, Tony Luck <tony.luck@...el.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [RFC] Display the cpu of sched domain in procfs

On 19/02/2020 09:13, Valentin Schneider wrote:
> Hi,
> 
> On 19/02/2020 07:15, Chen Yu wrote:
>> Problem:
>> sched domain topology is not always consistent with the CPU topology exposed at
>> /sys/devices/system/cpu/cpuX/topology,  which makes it
>> hard for monitor tools to distinguish the CPUs among different sched domains.
>>
>> For example, on x86 if there are NUMA nodes within a package, say,
>> SNC(Sub-Numa-Cluster),
>> then there would be no die sched domain but only NUMA sched domains
>> created. As a result,
>> you don't know what the sched domain hierarchical is by only looking
>> at /sys/devices/system/cpu/cpuX/topology.
>>
>> Although by appending sched_debug in command line would show the sched
>> domain CPU topology,
>> it is only printed once during boot up, which makes it hard to track
>> at run-time.

What about /proc/schedstat?

E.g. on Intel Xeon CPU E5-2690 v2

$ cat /proc/schedstat | head
version 15
timestamp 4486170100
cpu0 0 0 0 0 0 0 59501267037720 16902762382193 1319621004
domain0 00,00100001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 00,3ff003ff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 ff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

        ^^^^^^^^^^^

cpu1 0 0 0 0 0 0 56045879920164 16758983055410 1318489275
domain0 00,00200002 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 00,3ff003ff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 ff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
...