Re: NetBSD/vax current

[David Brownlee <abs%netbsd.org@localhost>]

On 20 April 2014 04:20, Anders Magnusson <ragge%ludd.ltu.se@localhost> wrote:
> [about NetBSD slowniness on vax]
>
> For someone who is curious; some time ago (about 15 years) I noticed that
> NetBSD had become very slow on 11/750; unreasonable slow compared to other
> machines.
>
> I started searching and found that quite much time were spent in hardclock.
> This is an effective way to make a slow machine much more sluggish.
>
> Here is a simple explanation for someone not a low-level hacker:
>
> Hardclock runs each 10ms.  We can say that it takes 500 instructions to
> complete.  On a 1 MIPS machine we will spend 10000 instructions between each
> hardclock interrupt, of which 9500 will be for user programs (~95%).  On a
> 1GIPS machine we have 10000000 instructions, of which 9999500 will be used
> for processes (~99.9%).
>
> Suddenly something is added that makes hardclock take 5000 instructions
> instead.  On the 1MIPS machine we now only have 50% of the CPU left, but on
> the newer machine we still have 99.9% of the CPU left (== not noticeable).
> Something like this can only be seen on a really slow machine, it's most
> likely not possible to find it even with fine-grain profiling on a modern
> PC.
>
> Back then, it turned out to be some NTP and timekeeping using long long
> calculations that did eat up hardclock.   Just commenting out this made the
> machine just as slow as before :-)

Would building a kernel with a lower HZ be a quick way to test?