Re: [Xen-devel] system time skew measurement patch

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 21/4/08 22:00, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> The patch below printk's useful interprocessor system time skew
> information.  Patch is relative to xen-unstable.  Printk is
> rate-limited to output only when O(max skew) grows.  Max skew
> is measured across all cores/processors... ideally eventually it
> should be measured for each processor and exported via "xm info"
> so groups of sync'ed processors can be properly identified.
> 
> Even on my Core 2 Duo E6850 @ 3.00 GHz (1 socket), I am seeing
> skew on the order of 6000 cycles (2 usec).  I'm not clear on
> whether this is due to the calibration algorithm or the
> hardware.

This is not unexpected. Stick a max() function at the end of get_s_time()
and we'll be fine.

 -- Keir



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