Re: [Xen-devel] [PATCH v2] use INT64_MAX as max expiration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.03.12 at 01:57, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
> Change from v1:
> According to Jan and Stefano's comments, drop the previous logic which 
> setting the value in an arbitrary way and use Stefano's suggestion instead.
> 
> Currently, the max expiration time is 2147483647ns(INT32_MAX ns)n This is 
> enough when guest is busy, but when guest is idle, the next timer will be 
> later than INT32_MAX ns. And those meaningless alarm will harm the pkg 
> C-state.
> 
> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> ---
>  vl.c |   11 ++++++-----
>  1 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/vl.c b/vl.c
> index be8587a..a9b7a0d 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1410,8 +1410,7 @@ static int64_t qemu_next_deadline(void)
>          delta = active_timers[QEMU_TIMER_VIRTUAL]->expire_time -
>                       qemu_get_clock(vm_clock);
>      } else {
> -        /* To avoid problems with overflow limit this to 2^32.  */
> -        delta = INT32_MAX;
> +        delta = INT64_MAX;

You're silently removing the comment - was it wrong (i.e. is there no
potential for overflow)? If so, this should be explained in the commit
message. If not, the change is wrong (quite possibly, using e.g.
1 << 48 might be an alternative then, but it needs to be clarified
what particular overflow is possible here, and that whatever new
value gets chosen doesn't trigger any).

Jan

>      }
> 
>      if (delta < 0)
> @@ -1427,9 +1426,11 @@ static uint64_t qemu_next_deadline_dyntick(void)
>      int64_t rtdelta;
> 
>      if (use_icount)
> -        delta = INT32_MAX;
> -    else
> -        delta = (qemu_next_deadline() + 999) / 1000;
> +        delta = INT64_MAX;
> +    else {
> +        delta = qemu_next_deadline();
> +        delta = (delta / 1000) + (delta % 1000 > 0 ? 1 : 0);
> +    }
> 
>      if (active_timers[QEMU_TIMER_REALTIME]) {
>          rtdelta = (active_timers[QEMU_TIMER_REALTIME]->expire_time -
> --
> 1.7.1




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