[Cryptography Team] Help with Processor Scheduling

[Michael van der Gulik]

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.