Re: dynamic-hz

[Nish Aravamudan <nish.aravamudan@gmail.com>]

On Mon, 13 Dec 2004 12:47:37 +0100, Andrea Arcangeli <andrea@suse.de> wrote:
> On Mon, Dec 13, 2004 at 03:25:21AM -0800, Andrew Morton wrote:
> > We still have 1000-odd places which do things like
> >
> >       schedule_timeout(HZ/10);
> >
> > which will now involve a runtime divide.  The propagation of msleep() and
> > ssleep() will reduce that a bit, but not much.
> 
> The above is by far the least cpu-hungry piece, it's going to sleep for
> 100msec, so any order-of-nanoseconds computation in such path will be by
> defininition not measurable.
> 
> msleep and ssleep as well will obviously be non measurable for the same
> reason (their only point is to wait and "waste" cpu). I mean,
> msleep/ssleep are the only places in the kernel that we don't really
> need to optimize ;).

I don't exactly understand what you mean by ""waste" cpu"? They both
give up the CPU by calling schedule_timeout() which calls schedule().
So any "waste" of the CPU is due to no tasks being available to run,
not to msleep()/ssleep(). I think :)

-Nish