linux-kernel - Re: posix-cpu-timers revamp

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Message-Id: <20080402194836.4933026F98A@magilla.localdomain>
Date:	Wed,  2 Apr 2008 12:48:36 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Frank Mayhar <fmayhar@...gle.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: posix-cpu-timers revamp

> One quick note:  this inline isn't needed for the 2b solution (allocate
> percpu storage in copy_signal CLONE_THREAD case), since if there's more
> than one thread there'll always be a percpu area and if there's only one
> thread the summation code won't be entered.

That's true.  I still think it's a good idea to have it, even if it winds
up being empty in the variants we really use.  The principle is that the
new set of types/functions could be used to implement exactly what we have
now.  In fact, it's usually best to do a series of small patches that start
with introducing the abstraction while not changing anything.

> And another quick note:  It appears that with the "allocate percpu
> storage in copy_signal CLONE_THREAD case" mechanism, I don't need to
> worry about allocating it anywhere else.  If I need it (which is only in
> the case of multiple threads and an interval timer) then I'll have it
> because it was allocated with the second thread.  

That's correct.

> So I just eliminate the allocation in do_setitimer() entirely.

Again, I'd leave the call to the inline that would do it.
For this implementation plan, its body is:
	BUG_ON(!task->signal->cputime.totals && !thread_group_empty(task));


Thanks,
Roland
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