Re: PHP performance on Xen domU with mulitple vcpu

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>>> and using a polling loop for uniquid is what I'd expect from php.
>> Whether or not it's good, bad, or just ugly, it looks to me as
>> though it's exposed a bug.
> Is it documented that gettimeofday has any particular resolution, or
> that successive values are unique?

Not a bug in the sense that gettimeofday is violating its interface
contract, just a bug in the sense that "something is wrong".  I'd say
gettimeofday() taking as long as a second, measured by ktrace records,
indicates a bug; everything involved is entirely in-kernel, so that
can't really be blamed on userland.

> I don't think it is, and I remember it being normal to have it
> increase by 10 ms at a time, back when it was really cool to have a
> microVAX III instead of a II.

Yes.  VAX timekeeping is rather bad by modern standards; many VAXen
(the KA630, used by the MicroVAX-II, in particular - I don't know the
MicroVAX-III in this regard) are not capable of better than 10ms.
There's no cycle counter and the ICCS can't do anything but an
interrupt every 10ms - NICR and ICR are subsetted away.

Ping from my (emulated) MicroVAX prints RTTs with approximately 10ms of
granaularity; I'm not sure why they're not all exactly 10ms
granularity, but I suspect it's the "increment the usec" behaviour.

Looking at the code, 1.4T's vax microtime() does an MFPR from the ICR
on everything but VAX46 (the VS 4k/60).  I don't see any statement in
the VARM that ICR must be implemented at all if interval timing is
subsetted out; presumably 1.4T depends on all processors it supports,
except VAX46, either fully implementing ICR or implementing it as
read-as-zero.

And, yes, here's that "increment the usec" behaviour:

	if (tvp->tv_sec == lasttime.tv_sec &&
	    tvp->tv_usec <= lasttime.tv_usec &&
	    (tvp->tv_usec = lasttime.tv_usec + 1) >= 1000000) {
		tvp->tv_sec++;
		tvp->tv_usec -= 1000000;
	}
	bcopy(tvp, &lasttime, sizeof(struct timeval));

Obviously, this depends on the system not sustaining as many as a
million fetches of the time (gettimeofday() being only one of variousp
things which can call microtime()) per second for any significant
period.

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