Messages in this thread | | | Date | Wed, 6 Jan 1999 20:58:25 +0100 (CET) | From | MOLNAR Ingo <> | Subject | Re: Can and should the kernel HZ value be changed? |
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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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