Re: clear_user_highpage()

["David S. Miller" <davem@redhat.com>]

On Thu, 12 Aug 2004 09:31:03 +1000
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> It would be nice, indeed, tho we have to be careful not to waste
> too much time in there looking for pages to clear, especially when
> there is none. Time spent not putting the CPU into power managed
> idle, at least on PPC's, means the CPU getting hotter, consuming
> more battery, etc... which is definitely a bad thing on laptops.

I totally agree.  This is why I believe it should be a per-arch
decision at cpu_idle() time whether to do the clears or not.

> I already took a significant hit with HZ=1000 btw, I'm considering
> lowering it back to 100 on ppc32 at least... We really want tickless
> scheduling for these beasts so we can select how deep to PM the CPU
> based on how much time we expect to stay idle.

I think dynamic-resolution timers are the way to go here.
Rusty was talking about something along theses lines at
the networking summit.

The reason Rusty had brought it up was due to a ipv6 problem,
there are some timers that need to get so far into the future
that with HZ=1000 it isn't representable in the 32-bit timer
offsets.  We have jiffies64 and could move the timer struct
over the a u64 for the offsets, but that seems like overkill.