Re: dynamic-hz

[Andrea Arcangeli <andrea@suse.de>]

On Mon, Dec 13, 2004 at 11:18:15AM +1100, Con Kolivas wrote:
> Thanks. I have to admit that the real reason I wrote this email was for 
> this discussion to go on record so that desktop users would not get 
> inappropriately excited by this change.

Sure, desktop doesn't need this, the reason somebody is asking for it,
is that the desktop stuff hurted some other non-desktop usages. Infact
my 2.4 tree was setting by default HZ=1000 if 'desktop' paramter was
passed to the kernel (so that I could lower the timeslice accordingly
too, without losing the effect of the nicelevels between nice 0 and
+19).

The other new case where I'm asked for this feature is again not the
desktop but the high end laptop with cpu throttling down to 80mhz, and
what Pavel mentioned about the lower consumption. Perhaps we could do
variable HZ there, though I doubt it has a pit that can be reprogrammed
with sane performance.

Very few people are going to get real benefit from HZ=1000, but
I certainly agree it worth to keep HZ=1000 on desktops since on a idle
machine the downside of the more frequent irq sure isn't measurable,
while having shorter timeslices may be visible with many tasks, and
shorter timeslices requires faster HZ to preserve the nicelevels.