Messages in this thread | | | Date | Thu, 01 Jul 1999 20:48:19 +0200 | From | Benno Senoner <> | Subject | Re: HZ and real-time performance |
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> > On Thu, Jul 01, 1999 at 02:24:21AM -0400, nunca wrote: > > I've been playing with writing real-time guitar effects boxes, and I've > > gotten the latency down to 11ms with stock linux. Would changing the HZ > > constant to 1024 help me reduce the latency (ie, does it cause a task to > > get scheduled more often)? Any other/better suggestions for decreasing > > latency? Thanks in advance. > > -Nolan > > I don't know what you are dpoing excatly, so I can't answer your question. > Latencies can not only be introduced by scheduling latency, but also by > interrupts holding spinlocks and similar. > > I'd suggest you try my HZ=400 patch from http://www.garloff.de/kurt/linux/ > (It not only sets the HZ value to 400, but also fixes the times reported to > userspace.) and test it out. > > Regards, > -- > Kurt Garloff <garloff@suse.de> SuSE GmbH, Nürnberg, FRG > Linux kernel development; SCSI driver: DC390 (tmscsim/AM53C974)
I found your patch some time ago, and modified it for 1000HZ , (changing all 4's to 10's :-) ) , and it works quite well but what are the implications (are these serious) of wrong times reported to userspace ? do you know which syscalls will report wrong times ?
PS: does anyone a reasonable upper limit to HZ on PII hardware ? will increase HZ too much lead to cache-performance drops, du too much context switching ?
I think 2000 would not degrade much the performance on a PII class system. (If i remember BeOS has 250usec scheduling latencies HZ=4000 ? )
regards, Benno.
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