Re: [Xen-devel] credit2 question

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.01.13 at 10:49, George Dunlap <george.dunlap@xxxxxxxxxxxxx> 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.

Oh, I wasn't thinking of just the optimization. It seemed wrong to
me to do the subtraction there in the first place: "time" is being
calculated from a plain value, so why would "ntime" be calculated
from a delta?

> Were you intending to submit a patch for this, or shall I?

I surely can do so, but first need to understand the intentions
of that code.

Jan


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