Re: [Gems-users] Ruby-Opal interface

[Luke Yen <lyen@xxxxxxxxxxx>]

>
> #ifndef FAKE_RUBY
> #ifdef  DEBUG_RUBY
>      if (requestType != X86_IFETCH) {
>        DEBUG("[%d] rubycache:: access %s 0x%0llx\n", m_id,
>                  memop_menomic(requestType), la_t lineaddr );
>        print();
>      }
>  #endif
>
>      // ruby may call opal api to change m_fastpath_hit's value
>      (*ruby_api->makeRequest)( m_id, lineaddr, m_block_size,
>                                requestType, vpc, priv );
>  #else
>      // complete the request about 25% of the time
>      if ( random() % 4 == 0 ) {
>        complete( lineaddr );
>      }
>  #endif
>
>      if ( m_fastpath_hit ) {
>        // hit in fast path
>        return HIT;
>      }
>
>  First, could someone explain to me what the FAKE_RUBY macro does ?
>  Now, assume this macro has not been defined anyway, meaning that the
>  makeRequest call gets executed. What I don't understand is the comment
>  just near the code saying that ruby may call opal api to change
>  m_fastpath_hit's value. Indeed, the m_fastpath_hit is tested just at the
>  end of the macro. I'v tried to look in Ruby's code where this variable
>  actually gets modified but I was not successful. Could you please
>  point me in Ruby's code where this variable gets modified ?
>
>  Thanks.

   FAKE_RUBY is used during the Opal tester, not during actual execution,
so you shouldn't worry about that section of code.

   Regarding the Opal/Ruby call sequence.  Notice the 3 lines preceding
the makeRequest:

  // if ruby does accept requests, try for a "fast path hit"
    m_fastpath_request     = lineaddr;
    m_fastpath_outstanding = true;
    m_fastpath_hit         = false;

  When makeRequest() is invoked, and fastpath hits are turned ON, what
happens is that on fastpath hits the hitCallback() informing Opal that
Ruby is done processing the request invokes complete() (also in
rubycache.C).  Here the first couple of lines from that function are as
follows:

 // check for fast path completion
  if ( m_fastpath_outstanding && physical_address == m_fastpath_request )
{
#ifdef DEBUG_RUBY
    DEBUG_OUT("[%d] rubycache:: fastpath complete 0x%0llx\n", m_id,
physical_address);
#endif
    m_fastpath_hit = true;
    return;
  }

   The m_fastpath_outstanding and m_fastpath_request are
set by the 3 lines before makeREquest(), so on fastpath hits this
condition should be true, thus setting the m_fastpath_hit flag.  Then
complete() returns control to access(), to the lines following
makeRequest.  There the m_fastpath_hit check should be true, allowing for
fastpath hits to return from access() with HIT.

   Luke