Re: [Xen-devel] credit2 question

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 24/01/13 09:49, George Dunlap wrote:
> On 24/01/13 07:40, Jan Beulich wrote:
> > George,
> >
> > I'm getting puzzled by the second c2t() invocation in
> > csched_runtime(): Why is the difference of credits being passed
> > here? Doesn't that (unless svc->credit is non-positive, i.e. in all
> > but unusual cases) guarantee time > ntime, and particularly
> > allow for negative ntime?
> Ah, right -- yes, if the other guys' credit is positive, "ntime" is 
> guaranteed to be lower.  Since c2t() involves integer division, it 
> would definiteyl be good to get rid of the extra call if we can.
> My general principle is to make the code clear and easily readable 
> first, and then do optimization afterwards -- in this case I just 
> never came back and did the optimization step.
> Were you intending to submit a patch for this, or shall I?
If we're doing optimization, we can probably get away with doing all of 
the calculation in "credit" (including the MIN/MAX checking), and then 
only do the conversion if we're not at one of those set points.  That 
should get rid of any integer division entirely in a large number of cases.
 -George

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel