Re: [Gems-users] question about XACT_LOG_BUFFER_SIZE parameter

[Jayaram Bobba <bobba@xxxxxxxxxxx>]

Ruben's approach seems better.
Add a beginEscapeAction() call in hardwareAbort()...

Jayaram Bobba wrote:
> Simplest fix would be to replace
>
> assert(m_escapeDepth[thread] >= 1)
> with
> if (m_escapeDepth[thread] < 1) return;
>
> in TransactionInterfaceManager.C:335
>
> Better fix would be to not implicitly end an escape action when using
> hardware rollback (in restartTransactionCallback()).
> We will try to fix it in the next release. Thanks for pointing it out.
>
> Jayaram
>
> cge@xxxxxxxx wrote:
> > Thank you for the response.
> >
> > When I set it to 256.
> > I got the following exception:
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > simics-common: log_tm/TransactionInterfaceManager.C:335: void  
> > TransactionInterfaceManager::endEscapeAction(int): Assertion  
> > `m_escapeDepth[thread] >= 1' failed.
> > Abort (SIGABRT) in main thread
> > The simulation state has been corrupted. Simulation cannot continue.
> > Please restart Simics.
> > Starting command line. (May have skipped commands in script files.)
> > [cpu3] v:0x0000000000011814 p:0x0003cf95814  magic (sethi 0x801, %g0)
> > Setting new inspection cpu: cpu3
> > Traceback (most recent call last):
> >    File "../../../gen-scripts/mfacet.py", line 308, in 
> > console_branch_internal
> >      wait_for_string(get_console(), __prompt)
> >    File  
> > "/s/csls05/csl/virtutech/simics-3.0.22/x86-linux/lib/python/text_console_common.py", 
> > line 10, in  wait_for_string
> >      wait_for_obj_hap("Xterm_Break_String", obj, break_id)
> >    File  
> > "/s/csls05/csl/virtutech/simics-3.0.22/x86-linux/lib/python/cli_impl.py", 
> > line  3371, in wait_for_obj_hap
> >      return wait_for_hap_common([hap_name, name, idx0])
> >    File  
> > "/s/csls05/csl/virtutech/simics-3.0.22/x86-linux/lib/python/cli_impl.py", 
> > line  3349, in wait_for_hap_common
> >      raise SimExc_Break, "Script branch interrupted"
> > sim_core.SimExc_Break: Script branch interrupted
> > Exception in python branch
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > There is an assertion fail in end_escape_action.
> > It does not happen if I set the buffer size to be small like 0 or 16.
> >
> > In ruby/simics/commands.C
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > if ((val == 0x122) && xact_mgr->shouldTrap(smt_thread_num)){
> >      // use software handler
> >      if (xact_mgr->shouldUseHardwareAbort(smt_thread_num)){
> >          xact_mgr->hardwareAbort(smt_thread_num);
> >      } else {
> >        xact_mgr->trapToHandler(smt_thread_num);
> >      }
> >    }
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > I think it is because setting the buffer size big enough will make
> > shouldUseHardwareAbort return true.
> > However, hardwareAbort does not call beginEscapeAction
> > while trapToHandler does.
> >
> > Any comments how to correct it?
> >
> > Thanks,
> > Cen
> >
> > Quoting Jayaram Bobba <bobba@xxxxxxxxxxx>:
> >
> >  
> > >  From the wiki,
> > > *
> > > XACT_LOG_BUFFER_SIZE*: (>=0) The size of a magical hardware log buffer.
> > > Used to perform 0-cycle restoration of memory values for any 
> > > transaction
> > > having logs not exceeding this buffer size.
> > >
> > > Basically, it allows zero-cycle aborts for small transactions.
> > >
> > > You would need a bigger log buffer for transactions to be able to use
> > > it. In LogTM-SE, each transaction starts
> > > off by writing a transaction header which itself is 68 bytes. So you
> > > would probably need something around 256 bytes
> > > to be useful...
> > >
> > > What kind of exception are you seeing when value is set to 1024?
> > >
> > > Jayaram
> > >
> > > cge@xxxxxxxx wrote:
> > >    
> > > > Hi,
> > > >
> > > > Does anyone know how can XACT_LOG_BUFFER_SIZE parameter enhance the
> > > > performance in
> > > > MESI_CMP_filter_directory protocol.
> > > > I tried to set the value to 16 or 32, and see no performance
> > > > difference in terms of cycles when running micro-program.
> > > >
> > > > Also when I set the parameter to a large value like 1024, an exception
> > > > will be thrown. Is there an allowable maximum value?
> > > >
> > > > Thanks,
> > > > Cen
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