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

[Dave Winchell <dwinchell@virtualiron.com>]

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
>  
>