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

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Date:   Wed, 19 Feb 2020 10:46:52 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Chen Yu <yu.chen.surf@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        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 10:00, Chen Yu wrote:
>> Now, if you have a userspace that tries to be clever and wants to use this
>> information then yes, this isn't ideal, but then that's a different matter.
> The dmesg might be lost if someone has once used dmesg -c to clear the log,
> and the /var/log/dmesg might not always there. And it is not common to trigger
> sched domain update once boot up in some environment.
> But anyway, this information printed by sched_debug is very fertile for knowing
> the topology.
>> I think exposing the NUMA boundaries is fair game - and they already are
>> via /sys/devices/system/node/node*/.
> It seems that the numa sysfs could not reflect the SNC topology, it just has the
> *leaf* numa node information. Say, node0 and node1 might form one sched_domain.

Right, but if you have leaves + distance table, then userspace can try to
be clever about it without being exposed to scheduler innards.