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Re: [Xen-devel] [PATCH] Fix hvm guest time to be more accurate

Eddie, Haitao:

The patch looks good with the following comments.

1. Since you are in missed_ticks(), why not increase the threshold
   to 10 sec?

2. In missed_ticks() you should only increment pending_intr_nr by missed_ticks
   calculated when  pt_support_time_frozen(domain).

3. You might as well fix this one too since its what we discussed and is so
   related to constant tsc offset:
     In pt_timer_fn, if !pt_support_time_frozen(domain) then
     pending_intr_nr should end up with a maximum value of one.

regards,
Dave


Dong, Eddie wrote:

Dave Winchell wrote:
Eddie,

I implemented #2B and ran a three hour test
with sles9-64 and rh4u4-64 guests. Each guest had 8 vcpus
and the box was Intel with 2 physical processors.
The guests were running large loads.
Clock was pit. This is my usual test setup, except that I just
as often used AMD nodes with more processors.

The time error was .02%, good enough for ntpd.

The implementation keeps a constant guest tsc offset.
There is no pending_nr cancellation.
When the vpt.c timer expires, it only increments pending_nr
if its value is zero.
Missed_ticks() is still calculated, but only to update the new
timeout value. There is no adjustment to the tsc offset
(set_guest_time()) at clock interrupt delivery time nor at re-scheduling time.

So, I like this method better than the pending_nr subtract.
I'm going to work on this some more and, if all goes well,
propose a new code submission soon.
I'll put some kind of policy switch in too, which we can discuss
and modify, but it will be along the lines of what we discussed below.

Thanks for your input!

-Dave



Haitao Shai may posted his patch, can u check if there are something
missed?
thx,eddie


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