Re: PHP performance on Xen domU with mulitple vcpu

[email protected] (Emmanuel Dreyfus) writes:

>This php function loops around gettimeofday() until the microsecond
>changes:
>  do {
>    (void)gettimeofday((struct timeval *) &tv, (struct timezone *) NULL);
>  } while (tv.tv_sec == prev_tv.tv_sec && tv.tv_usec == prev_tv.tv_usec);


Yes, that's the difference between precision and resolution.

While gettimeofday yields a value with a microsecond precision,
the resolution depends on the timecounter, and some timecounters
only provide a resolution of HZ ticks per second (usually 10ms).

Polling for a change therefore can take 10000 times a microsecond
and using a polling loop for uniquid is what I'd expect from php.