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SubjectRe: Can and should the kernel HZ value be changed?

On Tue, 5 Jan 1999, Egil Kvaleberg wrote:

> Pretty basal stuff, really: The more often you can switch context, the
> quicker the response will be for any given process residing down on the ready
> list somewhere. [...]

_no_. When it's needed, we already context switch with arbitrary frequency
(up to 360 thousand times per second on my box). Eg. when you hit a key in
pine (running on the same box) to write the reply mail, the 'keypress
event' gets to the application much much faster than 10 msec ...

> [...] The is pretty vital for any real-timeish application, and
> nicely visualized and obvious (as well as gratifying for ones sanity) when
> running X.

so, _why_ does it make a difference for X, and can you quantify it with
some reproducible testcase? It's not the number of context switches for
CPU-bound processes (this is what HZ really means), thats ludicrous.
(mouse events get to X just as fast as keyboard events) I do not say you
dont see a speedup, i'd just like to fix the real reason ...

my best guess is that menus and other widgets use low-value [mandatory]
select() timeouts, which translate into a 10-20msec delay. Changing HZ to
something more finegrained appears to the advanced user as a speedup. The
solution to this problem is not to change HZ, but rather to (maybe)
implement arbitrary precision timers. (which implmentation btw. already
exists)

-- mingo


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