Re: [Gems-users] About data prefetch

[Polina Dudnik <pdudnik@xxxxxxxxx>]

Dear Lori,

Like Dan said, there are some remains of what used to be prefetch code. I recommend you grep for prefetch and try to trace where it occurs and why. 

Besides that, you know as much as we do and you have all the necessary tools. Please come back with more specific questions.

Thank you.

Polina

On Sun, May 23, 2010 at 10:58 PM, lori zhuang <lorizhuang@xxxxxxxxx> wrote:

Dan, how can I add prefetching function in Ruby? I mean simulating the behavior of the prefetch instrutions. What should I refer to do this? Please give me a clue.

Thanks,

lorizhuang

On Fri, May 21, 2010 at 11:46 AM, lori zhuang <lorizhuang@xxxxxxxxx> wrote:

Thanks a lot, Dan!

Regards,

lorizhuang

 

Date: Thu, 20 May 2010 06:42:30 -0600
From: Dan Gibson <degibson@xxxxxxxx>
To: Gems Users <gems-users@xxxxxxxxxxx>
Subject: Re: [Gems-users] About data prefetch
Message-ID:
       <AANLkTilj__QDb7K4ooknV7X47bNYLbfYUlj3r_Mkkrcu@xxxxxxxxxxxxxx>
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Ruby currently ignores software prefetches, as you point out. At one time,
there was some internal code that did hardware prefetching, but I don't
think that was ever released (however, its remnants remain scattered here
and there, e.g., the prefetch bit).

Regards,
Dan

On Thu, May 20, 2010 at 12:30 AM, lori zhuang <lorizhuang@xxxxxxxxx> wrote:

> List,
>      I wonder if Ruby simulates the behavior of data prefetch. It seems
> like it does according to this link
> https://lists.cs.wisc.edu/archive/gems-users/2007-November/msg00102.shtml.
> But it seems like it doesn't according to the code in SimicsDriver.C:
>
> int SimicsDriver::makeRequest(memory_transaction_t *mem_trans) {
>     ...
>     ...
>     //* skip unsupported types*
>     if (*isUnhandledTransaction*(mem_trans)) {
>     ret = Unhandled;
>     } else {
>      // perform makeRequest()
>       int proc = SIMICS_get_proc_no(mem_trans->s.ini_ptr);
>      ret = m_processors[proc]->makeRequest(mem_trans);
>    }
>    ...
>   ...
> }
>
> bool SimicsDriver::*isUnhandledTransaction*(memory_transaction_t*
> mem_trans) {
>   // only handle user data?
>   if (USER_MODE_DATA_ONLY) {
>     if(PRIV_MODE) {
>       return true;
>     }
>     if(mem_trans->s.type == Sim_Trans_Instr_Fetch) {
>       return true;
>     }
>   }
>
>   // no prefetches
>   if (mem_trans->s.type == Sim_Trans_Prefetch) {
>     return true;
>   }
>
>   // no cache flush
>   if (mem_trans->s.type == Sim_Trans_Cache) {
>     return true;
>   }
>
>   // no DMA & IO
>   if (IS_DEV_MEM_OP(mem_trans->s.ini_type) ||
>       IS_OTH_MEM_OP(mem_trans->s.ini_type) ||
>       mem_trans->s.physical_address >
> uinteger_t(RubyConfig::memorySizeBytes())
>      ) {
>     return true;
>   }
>
>   return false;
> }
>
> Ruby skips supported types memory request and it threats Sim_Trans_Prefetch
> as unsupported types. Hence I think Ruby doesn't simulates data prefetching.
> Am I right?
> Since I'm going to add a prefetch instruction of the SPARC v9 instruction
> set to a benchmark and see if any speedups. That's why I care so much about
> prefetching. Any suggestion is highly appreciated.
>
>
> Thanks,
> lorizhuang
>
>
>
>
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>
>


--
http://www.cs.wisc.edu/~gibson [esc]:wq!

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