Re: Process Control Extensions

John,

ok, I guess that now we arrives in dangerous territory, and this is the
limitation of using priority hints for testing process order.

For testing process order, you need to "rely" on the scheduler actually
implementing the priorities, because no one would want to do such testing
on a non-priority aware scheduler (as that would be useless).

And so comes this need for a priority_implemented() function.
But in which situations should this function return true?

We can have a loose definition which would say:

priority_implemented() will return true if the simulator "tries" to to
execute before
process with higher priority (but there is not formal guarantee),

or a more formal "hard" definition:

priority_implemented() will return true if the simulator executes in
each delta
cycle the processes in the order of decreasing priorities.

The risk of the latter option is that people may write programs that
could refuse to execute
if the scheduler is not priority aware, and that may then completely
rely on the priority
for correct execution of their program.
And then we have transformed the priorities "hints" into elements to can
be used
by the programmer.

So to me, either:

- we don't highlight the possible use of priorities for testing bugs
linked to process
ordering, and we don't have to provide any stuff related to randomization,

or

- we tell people that it is possible to do some variations on the
process order by using
random process priorities, we add randomization related stuff, and the
priority_implemented()
function (or maybe is_priority_aware() or something) but we voluntarily
tell the user that no
strong formal ordering is guaranteed by the implementation even if the
function returns true.

What do you think?

Jerome

On 5/14/2010 3:09 PM, john.aynsley@doulos.com wrote:
> Jerome,
>
> Right. So regardless of whether we add any features for randomization
> or repeatable randomization, it sounds like we might benefit from adding:
>
> bool *priority_implemented*() const;
>
> ???
>
> John A
>
>
>
> From: Jerome CORNET <jerome.cornet@st.com>
> To: john.aynsley@doulos.com
> Cc: "systemc-p1666-technical@eda.org" <systemc-p1666-technical@eda.org>
> Date: 14/05/2010 13:23
> Subject: Re: Process Control Extensions
>
>
> ------------------------------------------------------------------------
>
>
>
> Hi John,
>
> good point!
> Indeed, exploring the various possible process execution orders allows
> to discover bugs both in the platform synchronization
> and in the embedded software (in the TLM case). I did not push for
> this usage as we have other means of testing this (with full
> coverage, which randomization does not guarantee), but clearly it
> could anyway be a benefit (rather than always getting the same process
> order).
> However, we have to be careful with allowing a reproducible
> randomization from one run to the other. I would default to "same process
> order" by default, and add an option (command line, for instance) to
> change the random seed.
> The other problem in using this feature for testing is to know whether
> the simulator is priority-aware or not, else testing
> with different random priorities is obviously useless.
>
> Jerome
>
>
>
> On 5/14/2010 1:23 PM, _john.aynsley@doulos.com_
> <mailto:john.aynsley@doulos.com> wrote:
> Jerome,
>
> Does ST foresee the process priority hint being used as a way to
> produce pseudo-random process execution order within an evaluation
> phase as a way of improving test case coverage? If this were the case
> then a simulator that supports the "priority hint" would have superior
> capability going beyond mere simulation speed.
>
> I don't see a problem with this. We could even add a
> set_priority_random() !
>
> John A
>
>
> From: Jerome CORNET _<jerome.cornet@st.com>_
> <mailto:jerome.cornet@st.com>
> To: "Jeremiassen, Tor" _<tor@ti.com>_ <mailto:tor@ti.com>
> Cc: Stuart Swan _<stuart@cadence.com>_ <mailto:stuart@cadence.com>,
> _"john.aynsley@doulos.com"_ <mailto:john.aynsley@doulos.com>
> _<john.aynsley@doulos.com>_ <mailto:john.aynsley@doulos.com>,
> _"systemc-p1666-technical@eda.org"_
> <mailto:systemc-p1666-technical@eda.org>
> _<systemc-p1666-technical@eda.org>_
> <mailto:systemc-p1666-technical@eda.org>
> Date: 11/05/2010 09:19
> Subject: Re: Process Control Extensions
>
>
>
> ------------------------------------------------------------------------
>
>
>
> Tor, all,
>
> sorry, my explanation was lacking real-world numbers which I will fix
> right away.
> So, I will take again the example of a SystemC TLM platform
> interacting with an IP mapped on
> a hardware emulator. We have many such platforms at ST. Let us
> consider the following scenario:
> the system produces images in loop. To do this it depends on results
> computed by the IP mapped on
> the emulator, as well as computations performed by the embedded
> software itself. In other words,
> the embedded software "delegates" part of the computation to the IP in
> the emulator, then perform
> its own duties.
> It takes some time for the hardware IP to perform its computation and
> send back the result. In our
> typical case, we are at around 1 fps (depends on the frame resolution).
> And on the embedded software front, we are now running into situations
> where the embedded software
> execution itself takes more and more time. All in one, this results in
> increased workstation time taken
> to complete an evaluation phase of the scheduler (as the main process
> executing the embedded software
> is taking more and more time). In some situations, the evaluation
> phase takes more than one second (1.6
> to be precise).
> The result of the benchmark really depends on the process order
> execution chosen by the scheduler, and may change
> if you add other processes in the loop. But it is obvious that we have
> to prioritize the processes that will result
> in the IP on emulator starting its computations, as the sooner it will
> start the better. The worst case is if the emulator
> starts at the end of the evaluation phase, as we then add 1 second of
> penalty waiting for the result. With the numbers
> I given that is one second in addition to 1.6 already taken by the
> SystemC simulation. So in this example we can gain
> (or lose depending on which side you look at it) up to 62 % percent
> per evaluation phase. Process priorities ensures
> that you will never lose anything, whatever the process execution
> order is, and provided you have got a "priority-aware"
> simulator.
>
> I have focused here on the hardware emulator example, but there is
> room to exploit this feature in many other
> situations.
>
> Regards,
>
> Jerome
>
> On 5/8/2010 5:43 AM, Jeremiassen, Tor wrote:
> I'm not going to oppose this, but has ST done any benchmarking with
> respect to the utility of such a proposal? It would be good to have
> some quantitative idea of the possible performance benefit before
> making it part of the standard.
>
> Best regards,
>
> Tor Jerermiassen
>
> ---
> Tor Jeremiassen, Ph.D.
> Simulation and Modeling CTO
> SDO Foundational Tools
> Texas Instruments Ph: 281 274 3483
> P.O. Box 1443, MS 730 Fax: 281 274 2703
> Houston, TX 77251-1443 Email: _tor@ti.com_
> <mailto:tor@ti.com>
>
>
> ------------------------------------------------------------------------
>
> *
> From:* _owner-systemc-p1666-technical@eda.org_
> <mailto:owner-systemc-p1666-technical@eda.org>
> [_mailto:owner-systemc-p1666-technical@eda.org_] *On Behalf Of *Stuart
> Swan*
> Sent:* Friday, May 07, 2010 11:58 PM*
> To:* _john.aynsley@doulos.com_ <mailto:john.aynsley@doulos.com>;
> _systemc-p1666-technical@eda.org_
> <mailto:systemc-p1666-technical@eda.org>*
> Subject:* RE: Process Control Extensions
>
> John, All-
>
> I think I'm in favor of the process priority "hints", as long as it is
> absolutely clear in the standard that they are just
> hints and that a compliant implementation is always free to ignore them.
>
> Thanks
> Stuart
> *
> From:* _owner-systemc-p1666-technical@eda.org_
> <mailto:owner-systemc-p1666-technical@eda.org>
> [_mailto:owner-systemc-p1666-technical@eda.org_] *On Behalf Of
> *_john.aynsley@doulos.com_ <mailto:john.aynsley@doulos.com>*
> Sent:* Friday, May 07, 2010 4:00 AM*
> To:* _systemc-p1666-technical@eda.org_
> <mailto:systemc-p1666-technical@eda.org>*
> Subject:* RE: Process Control Extensions
>
> All,
>
> Does anyone have any specific objections or counter-proposals
> concerning the Process Control Extensions, or is everyone positive
> about them as they stand? (Of course, I am not trying to rule out any
> improvements or clarifications as we refine the spec.)
>
> How about ST's proposal for process priorities as hints? Adding actual
> process priorities to SystemC would seem to be a radical change that
> would impact the scheduler, process control, and might introduce the
> possibility of new use models. On the other hand, ST's proposal is
> only for "hints", in which case, do we want to change the IEEE
> standard "merely" to incorporate scheduler optimization hints?
>
> Thanks,
>
> John A
>
>
> -----Stuart Swan _<stuart@cadence.com>_ <mailto:stuart@cadence.com>
> wrote: -----
> To: _"john.aynsley@doulos.com"_ <mailto:john.aynsley@doulos.com>
> _<john.aynsley@doulos.com>_ <mailto:john.aynsley@doulos.com>,
> _"systemc-p1666-technical@eda.org"_
> <mailto:systemc-p1666-technical@eda.org>
> _<systemc-p1666-technical@eda.org>_
> <mailto:systemc-p1666-technical@eda.org>
> From: Stuart Swan _<stuart@cadence.com>_ <mailto:stuart@cadence.com>
> Date: 05/06/2010 10:05PM
> Subject: RE: Process Control Extensions
> John-
>
> Some quick answers embedded below to your questions..
>
> Thanks
> Stuart
> *
> From:* _owner-systemc-p1666-technical@eda.org_
> <mailto:owner-systemc-p1666-technical@eda.org>
> [_mailto:owner-systemc-p1666-technical@eda.org_] *On Behalf Of
> *_john.aynsley@doulos.com_ <mailto:john.aynsley@doulos.com>*
> Sent:* Wednesday, May 05, 2010 7:18 AM*
> To:* _systemc-p1666-technical@eda.org_
> <mailto:systemc-p1666-technical@eda.org>*
> Subject:* Process Control Extensions *
> Issues/Questions*
>
> * Should we now deprecate SC_CTHREAD or keep SC_CTHREAD as a
> first-class feature of SystemC, or something else?
> SC_CTHREAD has been around for so long that it won't go away anytime
> soon. One option is to say something in the LRM such as "SC_CTHREAD
> is now redundant since all of its features are now available with
> SC_THREAD, so SC_CTHREAD may be deprecated and removed from the standard
> at some point in the future."
>
> * Should we invite input from the members of the OSCI Synthesis WG on
> the subject of clocked threads and synchronous and asynchronous resets?
>
> * ST (Jerome) has proposed that we add process priorities. Does this
> P1666 WG wish to pursue that proposal? If so, how do process
> priorities interact with the process control extensions?
>
> If I understood Jerome's proposal, the priorities are just "hints" and
> can always be ignored. So it seems to me one option is to say that
> from the perspective
> of the process control extensions, the priorities have no implications
> on the standard.
>
> * Is include_descendants intended to find descendents of intermediate
> processes that have already terminated, i.e. children of dead children?
> I think it is supposed to get them all, Bishnupriya needs to confirm.
>
> * Do we need to try out these ideas in a proof-of-concept
> implementation, particularly given that the process control extensions
> are already (at least partially) implemented in the OSCI POC
> simulator? I will volunteer to create a set of regression tests.
> We accept your offer! Having such openly available tests will be very
> helpful in getting the features implemented properly in all simulators.
> We have donated some tests for process control constructs to OSCI.
> More tests are clearly needed. We have also implemented all of the
> constructs
> in our simulator and will run any tests that people offer against our
> implementation and provide the log results.
>
>
> John A
>
>
>
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