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

Andrea Arcangeli
2004-12-15T09:19:47Z

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.

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)