linux-kernel - Re: [PATCH 12/14] sched: make dl_bw a sub-quota of rt

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Message-ID: <525D1234.5060001@gmail.com>
Date:	Tue, 15 Oct 2013 12:00:20 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	rostedt@...dmis.org, oleg@...hat.com, fweisbec@...il.com,
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	bruce.ashfield@...driver.com--no-chain-reply-to
Subject: Re: [PATCH 12/14] sched: make dl_bw a sub-quota of rt_bw

On 10/14/2013 04:06 PM, Ingo Molnar wrote:
> 
> * Juri Lelli <juri.lelli@...il.com> wrote:
> 
>> +#ifdef CONFIG_SMP
>> +		struct dl_bw *dl_b = &cpu_rq(i)->rd->dl_bw;
>> +#else
>> +		struct dl_bw *dl_b = &cpu_rq(i)->dl.dl_bw;
>> +#endif
> 
>> +#ifdef CONFIG_SMP
>> +		struct dl_bw *dl_b = &cpu_rq(i)->rd->dl_bw;
>> +#else
>> +		struct dl_bw *dl_b = &cpu_rq(i)->dl.dl_bw;
>> +#endif
> 
> Btw., this kind of SMP/UP assymetry pattern really sucks. Why not make UP 
> use the SMP data structure, even if it's degenerate?
> 

Yes, I don't like it either, but that comes from the fact that it seemed to me
that, semantically, bandwidth for -deadline tasks has to be associated to the
single runqueue in UP and to the root_domain for SMP. In UP root_domain is
compiled out, so I'm not sure to understand what you suggest. I could probably
let dl_bw live on runqueues with the assumption that all the runqueues from the
same root_domain have the same dl_bw, that represents the dl_bw of the
root_domain. But I don't like this replication either :(.

Thanks,

- Juri
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