Re: [Gems-users] Processor Lost

[Dan Gibson <degibson@xxxxxxxx>]

As a corollary to this discussion, I'd like to add that this kind of 
issue is one of the reasons that full-system simulation is a great thing 
-- this sort of thing can happen to a real workload, too.
James Wang wrote:
> Hi Dan:
>     Thank you very much for your prompt reply. But I don't really understand what the nature of this situation is. Why would the OS want to deschedule my 
> benchmark? 
The OS deschedules threads for a variety of reasons. Interrupts of any 
kind typically need to be handled, and if your benchmark initiates a 
blocking I/O operation the OS will probably deschedule your benchmark 
while the I/O completes (including, say, page faults). Moreover, there 
is always the real-time interrupt timer that the OS uses for timesharing 
anyway -- this timer can actually be a problem when running with Simics, 
as a common trick is to set Simics's clock frequency low to improve I/O 
performance -- with low clock frequencies, timer interrupts happen more 
often relative to higher Simics frequencies. For other reasons, have a 
look at your favourite OS textbook.
> Also, I bound the thread to the processor, should it just stay there and run? 
See Kevin's response. In general, processor_bind() is a suggestion, not 
a command, to the OS.
> I did this with a four processor simulated machine, why other processors
> are not affected by this problem? 
>   
Solaris seems to favor P0 for a variety of reasons, chief among them 
simplicity.
>  
> Regards
> James
>   
Regards,
Dan
> ----- Original Message ----
> From: Dan Gibson <degibson@xxxxxxxx>
> To: Gems Users <gems-users@xxxxxxxxxxx>
> Sent: Friday, May 4, 2007 1:03:42 AM
> Subject: Re: [Gems-users] Processor Lost
>
> The OS could be descheduling your transactional benchmark, though I'm 
> not sure why that might be happening. Try quiescing the system by 
> killing background processes, and then pre-fetch any binaries or data 
> you might be using in your benchmark by running it once to completion 
> before loading Ruby (and hence, without synchronization). That should 
> eliminate any I/O you might inadvertenly cause at runtime. It will also 
> cause your benchmark to run with different system interactions, and will 
> hopefully fix the Processor Lost/Processor Found problem.
> Regards,
> Dan
>
> James Wang wrote:
>
>   
> > Hi All:
> >    I am running some transactional memory benchmark using a customized SMP cache coherent protocol. For some reason, p0 will run code other than the transactional benchmark and the other processors finishes fine. I cannot really tell what p0 is doing. I tried a few different random seed, the same situation happens every time. 
> >    Any idea?
> >    Thanks for any reply in advance.
> >
> > Regards
> > James
> >
> >
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