Messages in this thread | | | Date | Mon, 13 Dec 2004 00:42:56 +0100 | From | Pavel Machek <> | Subject | Re: dynamic-hz |
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Hi!
> >The overhead is a single l1 cacheline in the paths manipulating HZ > >(rather than having an immediate value hardcoded in the asm, it reads it > >from a memory location not in the icache). Plus there are some > >conversion routines in the USER_HZ usages. It's not a measurable > >difference. > > Just being devils advocate here... > > I had variable Hz in my tree for a while and found there was one > solitary purpose to setting Hz to 100; to silence cheap capacitors. > > The rest of my users that were setting Hz to 100 for so-called > performance gains were doing so under the false impression that cpu > usage was lower simply because of the woefully inaccurate cpu usage > calcuation at 100Hz. > > The performance benefit, if any, is often lost in noise during > benchmarks and when there, is less than 1%. So I was wondering if you > had some specific advantage in mind for this patch? Is there some > arch-specific advantage? I can certainly envision disadvantages to lower Hz.
Actually, I measured about 1W power savings with HZ=100. That's about as much as spindown of disk saves... Pavel -- People were complaining that M$ turns users into beta-testers... ...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl! - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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