Re: [PATCH 13/15] sched: add bandwidth management for sched_dl.

[Juri Lelli <juri.lelli@gmail.com>]

Hi,

On 05/25/2012 12:38 PM, Peter Zijlstra wrote:
> On Wed, 2012-05-23 at 23:42 +0200, Juri Lelli wrote:
>> +/*
>> + * Coupling of -dl and -rt bandwidth.
>> + *
>> + * Here we check, while setting the system wide bandwidth available
>> + * for -dl tasks and groups, if the new values are consistent with
>> + * the system settings for the bandwidth available to -rt entities.
>> + *
>> + * IOW, we want to enforce that
>> + *
>> + *   rt_bandwidth + dl_bandwidth<= 100%
>> + *
>> + * is always true.
>> + */
>
> I was thinking we could do it the other way around, have have
> dl_bandwidth included in rt_bandwidth.
>

If I understand correctly, you are proposing to treat -dl tasks as a
special case of "real-time" tasks. Then we could reserve some bw to
"real-time" (rt_bandwidth cap) activities and give a piece of this
bw to -dl tasks (what remains is for -rt tasks). This is in principle
nice and useful, but I'm not quite sure that this is the right point
to achieve this logical behavior.
I mean, -dl and -rt tasks are separately treated, so it is probably
cleaner to manage their knobs separately. They have to coexist rather
than be considered one a sub-case of the other. A better way to go
for a common cap for them is probably the (long-term) hierarchical
scheduling mechanism.

So, I would prefer to keep the interface as is for now, but I can also
completely misunderstood your thoughts :-P.

Thanks and Regards,

- Juri