[PTLsim-devel] Prefetching

Fri Jun 29 10:21:09 EDT 2007

Yes - we do have Intel Core Duo style prefetchers and more for L1, L2 in 
an internal version.
-Kanad

On Fri, 29 Jun 2007, Matt T. Yourst wrote:

> On Thursday 28 June 2007 11:58, Stephan Diestelhorst wrote:
>> Hi again,
>>   thanks for the previous fixes, helps and of course for making this
>> massive simulator!
>>
>> I'm still digging through this project and got another question:
>>
>> Are any of the PREFETCH instrucitons actually acted upon? As far as I can
>> see, they decode to ld.pre, which in uopimpl.cpp resolves to a nop, as it
>> should be handled by the simulation core, just like the loads.
>>
>> The cache itself provides hooks for prefetching, such as
>> CacheHierarchy::initiate_prefetch() (in dcache.cpp) but I do obviously miss
>> the connection between the issue-queue and the cache-model.
>>
>> For ordinary cache-misses it works like this: ReorderBufferEntry::issue ->
>> ReorderBufferEntry::issueload -> CacheHierarchy::issueload_slowpath ->
>> MissBuffer::initiate_miss
>>
>> Is my assumption of PREFETCH=nop correct? Would be glad to get any pointer!
>>
>
> I thought for sure we had a method called issueprefetch() in smtexec.cpp that
> served this purpose, but apparently it was removed for some reason or never
> made it into the official version. I'm looking for that code now (I think one
> of our development team members added it to some older project specific
> internal version of PTLsim and forgot to port it over).
>
> It should be fairly easy to add back in: CacheHierarchy.initiate_prefetch()
> does what you want. You could add a new function like
> ReorderBuffer.issue_prefetch() to start the prefetch based on the physical
> address generated by any OP_ld_pre uops (the cache level is in
> uop.cachelevel, for PREFETCHTn). Just make a copy of
> ReorderBufferEntry.issueload() and remove everything except the address
> generation logic.
>
> - Matt
>
> -------------------------------------------------------
> Matt T. Yourst                    yourst at peptidal.com
> Peptidal Research Inc., Co-Founder and Lead Architect
> -------------------------------------------------------
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