linux-kernel - Re: Sched_class documentation

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Message-ID: <1276794788.27822.603.camel@twins>
Date:	Thu, 17 Jun 2010 19:13:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	sebastiano spicuglia <spicuglia.sebastiano@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: Sched_class documentation

On Thu, 2010-06-17 at 19:02 +0200, sebastiano spicuglia wrote:
> Hi Ingo,
> 
> I made many progress. But I have two doubts yet.
> First: what does hrtick_start do?

higher resolution ticks

> I think that: if I call hrtick_start(rq, 500)  then, after 500ns, the
> task_tick function will be invocated.
> Is it right?

Yep, instead of waiting for the next system tick is programs a hrtimer
to deliver it -- its disabled by default though, since programming
timers is rather expensive :/

> Second: if my schedule_class decides to preempt the current task, it
> has to call resched_task(rq->curr).
> Is it right?

Either that or resched_cpu(), depending on which is most convenient.

It sets TIF_RESCHED and possibly IPIs the remote CPU. The TIF flag is
then observed (on re-entry to userspace in case of the IPI) and we call
into schedule().
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