Re: [Gems-users] Tourmaline and scheduling

[Matthew James Horsnell <horsnelm@xxxxxxxxxxxx>]

Dan/Derek,

Thanks for your reply. I guess I probably didn't phrase my question well
enough. I appreciate that no performance results in LogTM were presented
using the tourmaline module. However, my question is equally applicable
to the Gems-Ruby modules; do you in any way alter the OS thread
scheduling policy in Solaris?. Using tourmaline, and although the ruby
modules will add timing delays, I see very infrequent overlapping of
transactional threads, mainly do to the influence that the OS scheduling
policy appears to have on the way the transactional threads are
scheduled. For example on a 4 processor system, I rarely see all
processors executing transactionally, and for long periods of time, only
one processor is executing a transactional thread.

Perhaps I am misunderstanding something, but currently with the OS
scheduling the transactional threads (in my case running the STAMP
kmeans benchmark) I hardly see any concurrency, not due to aborted
transactions but rather because the operating system is rarely choosing
to scheduling multiple transactional threads concurrently.

Any more information would be gratefully received,

Matt

Derek Hower wrote:
> Reply from Dan Gibson:
>
>
> Tourmaline is a functional transactional memory simulator, which is  
> intended to have extensible behavior for future expansion. Its  
> default behavior makes no attempt to model a realistic timing nor  
> interleaving of transactions -- it simply provides the bare minimum  
> implentation of atomicity in the most trivial, simulator-magic way  
> possible -- by literally disabling all (other) processors.
>
> To my knowledge, the released version of tourmaline has never been  
> used to collect viable research data -- it is a tool intended to  
> enable warm-up of transactional applications, as well as to  
> facilitate debugging of transactional applications seperate from the  
> debugging of the timing simulator.
>
> If you are interested in looking at running concurrent threads, you  
> should look into implementing sub-classes of TransactionController,  
> which Tourmaline uses to guarantee atomicity of transactions. There  
> is a how-to guide in the README for tourmaline, called the  
> 'Transaction Controller Cookbook'.
>
> Please note that the /timing/ runs for the LogTM family of work all  
> used Ruby, not Tourmaline. However, tourmaline is a viable tool for  
> (much) longer simulations at the cost of some timing fidelity.
>
> Regards,
> Dan
>
>
> On Sep 28, 2007, at 3:37 AM, horsnelm@xxxxxxxxxxxx wrote:
>
>> Hi,
>>
>> I've been looking at the code inside the tourmaline TM module of  
>> the gems
>> package. I'm trying to run some benchmarks, in particular the  
>> stamp-0.9.4
>> benchmarks, and wondered if you could comment on the scheduling  
>> policy and
>> how you have used tourmaline, or gems in general, to generate your
>> results.
>>
>> I can see in the tourmaline code, that when you begin a transaction  
>> you
>> disable interrupts in the processor registers, which means that  
>> until the
>> transaction resolves it cannot be interrupted. You switch back on
>> interrupts when the transaction commits or aborts.
>>
>> Is it not the case that the operating system threads will  
>> interleave with
>> the transactions, competing for the cpu time? Do you prevent this from
>> happening by changing the scheduling policy in the OS, or do you  
>> measure
>> your results in some other manner? The reason I ask, is that when  
>> running
>> say a 4 threaded application, on a 4 cpu architecture, transactions
>> infrequently overlap as they are scheduled according to the OS.  
>> Ideally
>> I'd like the transactional threads to run as concurrently as  
>> possible to
>> look at the interactions between them.
>>
>> Thanks,
>>
>> Matt Horsnell
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