Re: [PATCH 1/3] Added runqueue clock normalized with cpufreq

[Harald Gustafsson]

2010/12/17 Dario Faggioli <raistlin@xxxxxxxx>:
> On Fri, 2010-12-17 at 15:29 +0100, Peter Zijlstra wrote:
>> Solving the CPUfreq problem involves writing a SCHED_DEADLINE aware
>> CPUfreq governor. The governor must know about the constraints placed on
>> the system by the task-set. You simply cannot lower the frequency when
>> your system is at u=1.
>>
> We already did the very same thing (for another EU Project called
> FRESCOR), although it was done in an userspace sort of daemon. It was
> also able to consider other "high level" parameters like some estimation
> of the QoS of each application and of the global QoS of the system.
>
> However, converting the basic mechanism into a CPUfreq governor should
> be easily doable... The only problem is finding the time for that! ;-P

I'm a bit choked before the holidays, but I can fix this in the
beginning of next year.
At the same time as I do a new version of the current patches that takes
in Peter's comments.

>> The simple solution would be to slow down the runtime accounting of
>> SCHED_DEADLINE tasks by freq/max_freq. So instead of having:
>>
>>   dl_se->runtime -= delta;
>>
>> you do something like:
>>
>>   dl_se->runtime -= (freq * delta) / max_freq;
>>
>> Which auto-magically grows the actual bandwidth, and since the deadlines
>> are wall-time already it all works out nicely. It also keeps the
>> overhead inside SCHED_DEADLINE.
>>
> And, at least for the meantime, this seems a very very nice solution.
> The only thing I don't like is that division which would end up in being
> performed at each tick/update_curr_dl(), but we can try to find out a
> way to mitigate this, what do you think Harald?

Yes, I will do something like this instead, need to make sure that
everything is consider first though.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/