Re: Time goes crazy in 2.6.9 after long cli [was Re: USB making time drift]

Andrea Arcangeli
2004-12-16T11:14:15Z

On Thu, Dec 16, 2004 at 02:15:49AM +0100, Pavel Machek wrote:
> Okay, I have good news and bad news. Bad news is that it is broken on
> my machine, too. Good news is that breakage is not at all subtle.

Well, I was pretty sure it was reproducible since the PIT and TSC are
standard hw in all machines, it's just the excessive usb irq latency
that triggers only in a few machines like my firewall (only with
HZ=1000).

My suggestion is that first we fix the accuracy of this, and *then* we
consider switching to a one-short timer.

Fixing this is possible as well by using only the TSC accuracy to
account for system time, and not to use anymore the PIT accuracy as
source of accuracy for system time. But then any error calibration while
we transfer the accuracy of the PIT to the TSC, will propagate in a
cumulative way over time. So it's not clear to me we can do that safely.
The PIT is designed everywhere to be accurate for system time.