linux-kernel - Re: [PATCH 02/14] sched: add extended scheduling interface.

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Message-ID: <52833B95.7060700@gmail.com>
Date:	Wed, 13 Nov 2013 09:43:01 +0100
From:	Juri Lelli <juri.lelli@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
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	harald.gustafsson@...csson.com, vincent.guittot@...aro.org,
	bruce.ashfield@...driver.com
Subject: Re: [PATCH 02/14] sched: add extended scheduling interface.

On 11/12/2013 06:23 PM, Steven Rostedt wrote:
> On Thu,  7 Nov 2013 14:43:36 +0100
> Juri Lelli <juri.lelli@...il.com> wrote:
> 
> 
>> + * This is reflected by the actual fields of the sched_param2 structure:
>> + *
>> + *  @sched_priority     task's priority (might still be useful)
>> + *  @sched_deadline     representative of the task's deadline
>> + *  @sched_runtime      representative of the task's runtime
>> + *  @sched_period       representative of the task's period
>> + *  @sched_flags        for customizing the scheduler behaviour
>> + *
>> + * Given this task model, there are a multiplicity of scheduling algorithms
>> + * and policies, that can be used to ensure all the tasks will make their
>> + * timing constraints.
>> + *
>> + * @__unused		padding to allow future expansion without ABI issues
>> + */
>> +struct sched_param2 {
>> +	int sched_priority;
>> +	unsigned int sched_flags;
> 
> I'm just thinking, if we are creating a new structure, and this
> structure already contains u64 elements, why not make sched_flags u64
> too? We are now just limiting the total number of possible flags to 32.
> I'm not sure how many flags will be needed in the future, maybe 32 is
> good enough, but just something to think about.
> 
> Of course you can argue that the int sched_flags matches the int
> sched_priority leaving out any holes in the structure, which is a
> legitimate argument.
> 
>> +	u64 sched_runtime;
>> +	u64 sched_deadline;
>> +	u64 sched_period;
>> +
>> +	u64 __unused[12];
> 
> And in the future, we could use one of these __unused[12] as a
> sched_flags2;
> 
> I'm not saying we should make it u64, just wanted to make sure we are
> fine with it as 32 for now.
> 

I'd stick with the current declaration for exactly the points you have made.

What others think?

Thanks,

- Juri
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