[Cryptography Team] Help with Processor Scheduling

Sun Dec 31 23:30:10 UTC 2006

Hi Ron.

Happy New Year!

Processes in Squeak are pre-empted. Before every send bytecode, the 
interpreter checks if an interrupt flag has been set. If so, it 
re-schedules processes.

There's good information (essentially annotated code) in Chapter 29 of 
the Blue Book about which processes are scheduled next: 
http://users.ipa.net/~dwighth/smalltalk/bluebook/bluebook_chapter29.html#ControlPrimitives29. 
Essentially, there's an array of processor priorities, each with a list 
of processes waiting at that priority. I wouldn't personally have 
designed it that way.

As with Monitors, I don't actually understand them. I just use 
Semaphores, which I find easy to understand.

Cheers,
Michael.

Ron Teitelbaum wrote:

>Hi Michael,
>
>Thanks for the feedback.  I'm running on winXP.  
>
>I'm beginning to understand the Process model better.  I think the problem
>is what you suggested that the threads are not preempted.  What I have
>during my SUnit test is one long program.  I've added Processor yield all
>over and this seems to help some.  How exactly it chooses the threads is
>still a mystery to me.  I found Monitor which has a lot of very good
>functionality.  I'm using it to slice up my treads.
>
>The funniest part of all this is that my problem is with testing, not real
>life.  In real life the system would not be running a test, would only have
>a few threads to worry about and everything would have the processing it
>needs.  
>
>Thanks again for your help!
>
>Ron
>
>  
>
>>-----Original Message-----
>>From: cryptography-bounces at lists.squeakfoundation.org
>>[mailto:cryptography-bounces at lists.squeakfoundation.org] On Behalf Of
>>Michael van der Gulik
>>Sent: Sunday, December 24, 2006 3:00 PM
>>To: Cryptography Team Development List
>>Subject: Re: [Cryptography Team] Help with Processor Scheduling
>>
>>Ron Teitelbaum wrote:
>>
>>    
>>
>>>Hi All,
>>>
>>>I was wondering if someone could help me answer a processor scheduling
>>>question. I'm running a process to test SSL memory. The data is
>>>received by a process running in a thread priority 40. The server is
>>>running priority 70. (both in the same image). There is one thread
>>>started as dataHandler for each send.
>>>
>>>When I run normally everything works fine. I send data and the
>>>dataHandler process picks it up and closes down. I'm seeing one send
>>>and about one receive before another send. When it's all done
>>>everything sent was received.
>>>
>>>The problem is that when I leave squeak and click on any other
>>>application, what I see is lots of sends but only rarely a receive.
>>>Then the application usually freezes up and has lots and lots of
>>>sockets open.
>>>
>>>Can someone explain to me why a test running and processes scheduled
>>>would act so differently if I click on another application?
>>>
>>>I tried to look at Processor activePriority hoping that since UI was
>>>running at 40 that maybe active priority was raised when Squeak was
>>>not the top most application. It appeared to stay at 40.
>>>
>>>Thanks for your help and any suggestions on how to diagnose this
>>>      
>>>
>>problem.
>>    
>>
>>Hi Ron.
>>
>>Which platform and VM version? On Linux, there's a "-lazy" argument
>>which you can pass to the Squeak VM, which I assume pauses the VM.
>>That's not quite the same behaviour as you're seeing but could be
>>somehow related. On some versions of Windows, the OS will give the
>>active window a higher CPU priority than windows in the background.
>>
>>Also, I assume you're aware of Squeak's rather... interesting...
>>scheduling behaviour. A process will never be pre-empted by a process
>>running at a higher priority. Rescheduling also only ever happens when
>>some interrupt happens in Squeak - usual sources are timers and (I
>>assume) I/O from places such as the network.
>>
>>Try stopping the Morphic thread ("the UI process") and observing the
>>behaviour of your program. Obviously you can't do this from Morphic, so
>>I recommend using a debugging tool I wrote called "REPLServer" available
>>from http://www.squeaksource.com/SecureSqueak. It could be that Morphic
>>is causing the reschedules, so that when Morphic stops causing process
>>reschedules, some of your threads never get scheduled to run . You could
>>force processes to be rescheduled by doing "Processor yield" in your code.
>>
>>I also find that bumping the event poll period gives me a more
>>responsive system when there are busy processes around, but I'm not sure
>>if it will affect your code. I'd be a bit wary if it did! It usually
>>means there's a bug:
>>
>>EventSensor eventPollPeriod: 50. "Makes the system more reactive under
>>load"
>>Sensor installEventTickler.
>>
>>And to start up REPLServer:
>>
>>" Telnet to localhost:4445 when the GUI freezes up. "
>>REPLServer startOn: 4445 named: 'REPLServer' priority: (Processor
>>highIOPriority).
>>
>>Michael.
>>_______________________________________________
>>Cryptography mailing list
>>Cryptography at lists.squeakfoundation.org
>>http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/cryptography
>>    
>>
>
>_______________________________________________
>Cryptography mailing list
>Cryptography at lists.squeakfoundation.org
>http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/cryptography
>
>
>
>  
>