Recent Problems with RELENG_7 i386
koitsu at FreeBSD.org
Thu Oct 9 10:07:31 PDT 2008
On Fri, Oct 10, 2008 at 03:51:02AM +1100, Ian Smith wrote:
> I see bf has since posted these values, but I'd already clipped stuff
> from the original post with kernel config and verbose dmesg, already
> wondering why the two didn't match, like:
> | options HZ=1000
> | options DEVICE_POLLING
> | CPU: AMD Athlon(tm) Processor (906.35-MHz 686-class CPU)
> | Timecounter "ACPI-safe" frequency 3579545 Hz quality 850
> | inittimecounter(0)... Timecounters tick every 10.000 msec
> ie HZ=100, as mentioned, and using ACPI-safe as later confirmed. So
> it's either a different kernel or bf updated kern.hz from loader.conf?
Yep -- his original mail had loader.conf shown, with this in it (near the
> > Well, I believe HZ was increased from 100 to 1000 long ago (RELENG_6?)
> > as a default. I'm really not sure of the implications of decreasing it,
> > besides having less granularity for some things (the only things I know
> > of would be something pertaining to firewalls, I just can't remember
> > what. My brain is full. :-) )
> You need a day off :) But yes, RELENG_5 still had HZ=100 default, long
> after the 'average' CPU clock frequency was 10 or more times faster than
> the 166MHz Pentiums and such (mostly then on only 100Mbps ethernet) that
> were comfortable at 100Hz slicing. 1000Hz was a big shift to catch up.
> In a day or so playing around with it years ago, I found 200-250Hz good
> for 300MHz, 500Hz a bit much, 1000Hz way too busy, and find my 1133MHz
> P3-M happy enough at 1000Hz, though I've done no specific tests on it.
> Some people had perhaps similar clock issues when their fast processors
> were throttling/stepping down to very low speeds (100, even 75MHz) while
> still slicing at 1000Hz, which I didn't find too surprising. Limiting
> minimum CPU freq to 300Mz or more seemed to solve many such issues, but
> I haven't your perseverance for digging up the relevant threads ..
> Even in 5.5-S (/sys/conf/NOTES and /sys/i386/conf/NOTES) HZ=1000 or 2000
> was suggested for DEVICE_POLLING (which bf included in config, though
> maybe it's not enabled?) and HZ=1000 or more was recommended when using
> DUMMYNET with ipfw - to provide smoother queue dispatching, I gather.
> Bottom line, IMHO, bf should probably run the default 1000Hz, 500 at
> least, on an Athlon 900. With powerd, maybe set min. freq >= 150MHz?
Wow, this is fantastic information. You've just educated me a great bit
about the history and use of HZ. I've always had a "general" idea of
its importance and key role, but I was never fully aware of the history.
P.S. -- I need more like 6 months off. I've never taken an official
(read: real) vacation my entire life. Maybe some day I'll get to travel
to Seoul and visit Pyun Yong-Hyeon and drink lots of soju. :-)
| Jeremy Chadwick jdc at parodius.com |
| Parodius Networking http://www.parodius.com/ |
| UNIX Systems Administrator Mountain View, CA, USA |
| Making life hard for others since 1977. PGP: 4BD6C0CB |
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