Re: Does Ada tasking profit from multi-core cpus?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 7 Mar 2007 23:21:04 -0600, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:1lq9zxgrnvfjx$.17ip3w3ei4xdb.dlg@40tude.net...
> ...
>> Just a side note, the Windows API GetThreadTimes (which the viewer
>> apparently uses) is corrupted. It counts complete time quants rather than
>> the  performance counter ticks. So, potentially you could observe 1% under
>> factual 99% CPU load. The bug should appear for threads performing much
>> synchronization, because they leave the processor before the current quant
>> expiration.
> 
> I wouldn't call it "corrupted"; it's just not very accurate (given that it
> can only register time with a granularity of 0.01 sec).

If it were just inaccurate then the obtained values would be like
ThreadTime + Error where Error has zero mean. That is just not the case.
ThreadTime has a systematic error => in my view corrupt. It simply does not
measure what its name assumes.

> I don't think there
> is any other way to find out CPU use, though, as the performance counter
> provides wall time and thus isn't very useful to find out how much a thread
> is running. (I've tried to figure out how to implement Ada.Execution_Time on
> Windows...)

Yes, at the user level there seems to be no way to do it. The performance
counter should be queried at the scheduling points, and the increment of
should be accumulated for the thread possessing the processor. Only the OS
kernel could do that.

Ada.Execution_Time looks quite a problem for Windows...

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de