Messages in this thread | | | Date | Sat, 9 Jan 1999 09:44:29 +0000 | From | Jamie Lokier <> | Subject | Re: Can and should the kernel HZ value be changed? |
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On Wed, Jan 06, 1999 at 08:58:25PM +0100, MOLNAR Ingo wrote: > On Tue, 5 Jan 1999, Egil Kvaleberg wrote: > > [...] 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)
Someone mentioned that rebuilding the kernel was significantly faster on their machine, with HZ == 400 instead of 100.
More rapid bottom-half handling is the only reason I can think of for that. Apart from different I/O characteristics, I'd expect the CPU-bound part of the compile to run _slower_ because of the increase in cache flushing.
-- Jamie
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