Re: USB making time drift [was Re: dynamic-hz]

From: Gene Heskett
Date: Wed Dec 15 2004 - 11:49:13 EST

On Wednesday 15 December 2004 04:17, Andrea Arcangeli wrote:
>On Tue, Dec 14, 2004 at 09:59:23PM -0500, Gene Heskett wrote:
>> Which way? I was running quite fast here, several minutes an
>In the future, if I disable the logic it goes in the past at the
> same speed it was previously going in the future.
>> hour, then I discovered the tickadj command, found its default
>> was 10000, and started reducing it. At 9926, I'm staying within
>> a sec an hour now. I have no idea when this started, I didn't
>That seems quite an hack, note I did an hack too and it make the
> drift much smaller (it gets manageable). But our modifications are
> wrong.
>The point is that this didn't happen with HZ=100, so it's not that
>tickadj is wrong, it's the tick adjustment code that doesn't work.
The HZ=1000 is the culprit?

>You may want to recompile your kernel with HZ=100 and verify it goes
>away (I didn't verify myself, but I verified the max irq latency I
> get is 4msec, and in turn I'm sure HZ=100 would fix it

Humm, that might also reduce the obviousness of the irq activity in
the audio, there are times when I can hear it very plainly while a
low level audio src is in use, like the sub-millivolt levels that come
out of my Hauppauge WinTV-GO+FM card. I keep having to turn the
master down to almost zip in order to keep it from sounding like I
have mice chewing in the walls, but its coming from the speakers.
Onboard AC-97 audio of course. Crappy stuff... Humm, 100HZ would
translate to 10 millisecond intervals. If you had a 4 millisecond
that would be spread over 4 of the 1000 hz interrupts. That sounds
rather confusing to the service routine I imagine.

I'll do that just for grins & report back.

Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
99.30% setiathome rank, not too shabby for a WV hillbilly attorneys please note, additions to this message
by Gene Heskett are:
Copyright 2004 by Maurice Eugene Heskett, all rights reserved.

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