> -----Original Message-----
> From: Greg Stark [mailto:[EMAIL PROTECTED]
> Sent: Monday, March 07, 2005 5:15 PM
> To: Dave Held
> Cc: Greg Stark; John A Meinel; Tom Lane; Magnus Hagander; Ken 
> Egervari;
> pgsql-performance@postgresql.org; [EMAIL PROTECTED]
> Subject: Re: [pgsql-hackers-win32] [PERFORM] Help with tuning 
> this query
> (with
> "Dave Held" <[EMAIL PROTECTED]> writes:
> > > What would be really neato would be to use the rtdsc (sp?) or 
> > > equivalent assembly instruction where available. Most
> > > processors provide such a thing and it would give much lower 
> > > overhead and much more accurate answers.
> > > 
> > > The main problem I see with this would be on multi-processor
> > > machines. (QueryPerformanceCounter does work properly on 
> > > multi-processor machines, right?)
> > 
> > I believe QueryPerformanceCounter() already does this.
> [...]
> Already does what? 
> Use rtdsc?


> In which case using it would be a mistake. Since rtdsc doesn't
> work across processors.

It doesn't always use RDTSC.  I can't find anything authoritative on
when it does.  I would assume that it would use RDTSC when available
and something else otherwise.

> And using it via QueryPerformanceCounter would be a non-portable
> approach to using rtdsc. Much better to devise a portable
> approach that works on any architecture where something equivalent
> is available.

How do you know that QueryPerformanceCounter doesn't use RDTSC
where available, and something appropriate otherwise?  I don't see
how any strategy that explicitly executes RDTSC can be called 

> Or already works on multi-processor machines? In which case, uh, ok.

According to MSDN it does work on MP systems, and they say that "it
doesn't matter which CPU gets called".

David B. Held
Software Engineer/Array Services Group
200 14th Ave. East,  Sartell, MN 56377
320.534.3637 320.253.7800 800.752.8129

---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
      joining column's datatypes do not match

Reply via email to