Re: [PATCHv12 0/3] rdmacg: IB/core: rdma controller support

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

Hello, Parav.

On Mon, Oct 10, 2016 at 06:43:59PM +0530, Parav Pandit wrote:
> > Also, I don't get what you mean by using percentage and when people
> > brought up this idea, it always has been stemming from
> > misunderstanding.  Can you please elaborate how percentage based
> > proportional control would work?  What would 100% mean when cgroups
> > can come and go?
>
> When 100% is given to one cgroup, all resources of all type can be
> charged by processes of that cgroup.
> Resources are stateful resource. So when cgroup goes away, they go
> back to global pool (or hw).
> Giving 100% to two cgroups is configuration error anyway (or without config).

That isn't proportional control.  That's using percentage as the unit
to implement absolute limits.  Proportional control implies work
conservation.

> As you know weight configuration allows automatic increase/decrease of
> resource to other cgroups when one of them go away, as opposed to
> absolute value. How this is going to work in exact terms for stateful

Hmm.... so are you saying that ti'd be work-conserving?  But what does
it mean to say "30%" and then have it all resources when there are no
other users.  Also, is it even possible to take back what have already
been allocated and are in use?

> Nop. Thats not true.
> (a) Every new resource has to be defined in cgroup_rdma.h
> (b) charge()/uncharge() has to happen by the cgroup for each.
> (c) Letting drivers do will make things fall apart. There are no APIs
> exposed either to let drivers know process cgroup either. There is no
> intention either.
> 
> (d) ratio means -if adapter has
> 100 resources of type - A,
> 80 resource of type - B,
> 
> 10% for cgroup-1 means,
> 10 resource of type - A
> 8 resource of type - B

So, this is not work-conserving.  There's too much confusion here.

Thanks.

-- 
tejun
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