parallel cost-centre profiling

[Simon Marlow]

On 10/06/10 18:06, Henrique Ferreiro wrote:
> Hi!
>
> I manage to make it work with one capability. That is, now the CCCS is
> stored per capability but I can't enable parallel profiling because
> the stacks are still shared.
>
> Now I wanted to have one instance of each stack and cost centre per
> capability, so that I can track the behaviour of each capability
> independently. Doing that is easy in the runtime system but I found
> out that I also have to change the code generator in the same way. I
> need "emitCostCentreDecl" and "costCentreStackDecl" to declare an
> array of structs instead of a single struct. Can someone help me with
> this?

Do you really need to do this?  Why not share the stacks and use a mutex 
to protect the operations?

Cheers,
	Simon


> 2010/6/4 Henrique Ferreiro<hferreiro at udc.es>:
>> Hi again!
>>
>> I need some help with this.
>>
>> 2010/3/17 Simon Marlow<marlowsd at gmail.com>:
>>> On 16/03/2010 19:34, Henrique Ferreiro wrote:
>>>>
>>>> Hello!
>>>>
>>>> I am trying to make cost centre profiling work in the threaded rts
>>>> build in order to use that information to better understand parallel
>>>> behaviour.
>>>>
>>>> Currently I am learning about the internals of GHC and I am thinking
>>>> about how this could be done. The main blocker is that the current
>>>> cost centre stack is a shared global variable. The simplest solution I
>>>> came up with is to convert it to a thread local variable. The problem
>>>> would be how to access it from the global timer.
>>>
>>> Yes, basically what you want to do is put CCCS into the StgRegs structure,
>>> which will make it thread-local.  In the timer signal you want to bump the
>>> counters for the CCCS on each Capability - so just iterate through the array
>>> of Capabilities and bump each one.
>>
>> I tried adding a new register CCCS to StgRegTable in stg/Regs.h but
>> there is too much hidden knowledge in the code and it isn't working.
>>
>> I got to the point where I have changed every reference to the global
>> variable to this register. The problem is that it isn't getting
>> updated. Debugging a bit it seems that the register is used as it
>> should (the calls to PushCostCentre and AppendCCS from the generated
>> code use the correct value in CCCS) but it isn't getting stored in the
>> register table because every time the timer is called, the value
>> stored is CCS_SYSTEM, the one used in initialization.
>>
>> I tried to mimic how the other registers are implemented but there is
>> no documentation at all so I wasn't sure what was exactly required.
>>
>> Could someone tell where exactly I have to change things or should I
>> post my changes and ask about specific details?
>>