Re: [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy

[Paul Turner]

On Mon, Aug 24, 2015 at 2:12 PM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello, Paul.
>
> On Mon, Aug 24, 2015 at 02:00:54PM -0700, Paul Turner wrote:
>> > Hmmm... I'm trying to understand the usecases where having hierarchy
>> > inside a process are actually required so that we don't end up doing
>> > something complex unnecessarily.  So far, it looks like an easy
>> > alternative for qemu would be teaching it to manage priorities of its
>> > threads given that the threads are mostly static - vcpus going up and
>> > down are explicit operations which can trigger priority adjustments if
>> > necessary, which is unlikely to begin with.
>>
>> What you're proposing is both unnecessarily complex and imprecise.
>> Arbitrating competition between groups of threads is exactly why we
>> support sub-hierarchies within cpu.
>
> Sure, and to make that behave half-way acceptable, we'll have to take
> on significant amount of effort and likely complexity and I'm trying
> to see whether the usecases are actually justifiable.  I get that
> priority based solution will be less precise and more complex on the
> application side but by how much and does the added precision enough
> to justify the extra facilities to support that?  If it is, sure,
> let's get to it but it'd be great if the concrete prolem cases are
> properly identified and understood.  I'll continue on the other reply.
>

No problem, I think the conversation is absolutely
constructive/important to have and am happy to help drill down.

> Thanks.
>
> --
> tejun
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