[6/7] Exit loop if we have been there too long

cheking each 64 pages is a random magic number as good as any other.
We don't want to test too many times, but on the other hand,
qemu_get_clock_ns() is not so expensive either.  We want to be sure
that we spent less than 50ms (half of buffered_file timer), if we
spent more than 100ms, all the accounting got wrong.

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 arch_init.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

On 05/22/2012 09:32 PM, Juan Quintela wrote:
> cheking each 64 pages is a random magic number as good as any other.
s/cheking/checking
> We don't want to test too many times, but on the other hand,
> qemu_get_clock_ns() is not so expensive either.  We want to be sure
> that we spent less than 50ms (half of buffered_file timer), if we
> spent more than 100ms, all the accounting got wrong.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  arch_init.c |   15 +++++++++++++++
>  1 files changed, 15 insertions(+), 0 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 76a3d4e..2aa77ff 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -296,6 +296,7 @@ int ram_save_live(QEMUFile *f, int stage, void *opaque)
>      uint64_t bytes_transferred_last;
>      double bwidth = 0;
>      int ret;
> +    int i;
> 
>      if (stage < 0) {
>          memory_global_dirty_log_stop();
> @@ -335,6 +336,7 @@ int ram_save_live(QEMUFile *f, int stage, void *opaque)
>      bytes_transferred_last = bytes_transferred;
>      bwidth = qemu_get_clock_ns(rt_clock);
> 
> +    i = 0;
>      while ((ret = qemu_file_rate_limit(f)) == 0) {
>          int bytes_sent;
> 
> @@ -343,6 +345,19 @@ int ram_save_live(QEMUFile *f, int stage, void *opaque)
>          if (bytes_sent == 0) { /* no more blocks */
>              break;
>          }
> +        /* we want to check in the 1st loop, just in case it was the 1st time
> +           and we had to sync the dirty bitmap.
> +           qemu_get_clock_ns() is a bit expensive, so we only check each some
> +           iterations
> +        */
> +        if ((i & 63) == 0) {
> +            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - bwidth) / 1000000;
> +            if (t1 > 50) { /* 50ms, half buffered_file limit */
can't we use a constant ?
> +                printf("big delay %ld milliseconds, %d iterations\n", t1, i);
printf ? 

Orit
> +                break;
> +            }
> +        }
> +        i++;
>      }
> 
>      if (ret < 0) {

Orit Wasserman <owasserm@redhat.com> wrote:
> On 05/22/2012 09:32 PM, Juan Quintela wrote:
>> cheking each 64 pages is a random magic number as good as any other.
> s/cheking/checking

Done.

>> +        */
>> +        if ((i & 63) == 0) {
>> +            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - bwidth) / 1000000;
>> +            if (t1 > 50) { /* 50ms, half buffered_file limit */
> can't we use a constant ?

50 is a constant already, no?  Or what do you mean.

>> +                printf("big delay %ld milliseconds, %d iterations\n", t1, i);
> printf ? 

This is the kind of "this shouldn't happen", but still happens, DPRINTF?

Thanks, Juan.

> >> +        if ((i & 63) == 0) {
> >> +            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - bwidth) / 1000000;
> >> +            if (t1 > 50) { /* 50ms, half buffered_file limit */
> > can't we use a constant ?
> 
> 50 is a constant already, no?  Or what do you mean.

  I guess Orit means,

#define THRESHOLD 50

if (t1 > THRESHOLD) { ... }

Regards,
chenwj

"(Wei-Ren Chen)" <chenwj@iis.sinica.edu.tw> wrote:
>> >> +        if ((i & 63) == 0) {
>> >> +            uint64_t t1 = (qemu_get_clock_ns(rt_clock) - bwidth) / 1000000;
>> >> +            if (t1 > 50) { /* 50ms, half buffered_file limit */
>> > can't we use a constant ?
>> 
>> 50 is a constant already, no?  Or what do you mean.
>
>   I guess Orit means,
>
> #define THRESHOLD 50
>
> if (t1 > THRESHOLD) { ... }

Thanks, Added.

Later, Juan.