config: Add memcheck stress test

Information
Submitter:	Andreas Hansson
Repository:	gem5
Branch:	default
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Description

Changeset 10705:bc21bfd38cbd
---------------------------
config: Add memcheck stress test

This is a rather unfortunate copy of the memtest.py example script,
that actually stresses the system with true sharing as opposed to the
false sharing of the MemTest. To do so it uses TrafficGen instances to
generate the reads/writes, and MemCheckerMonitor combined with the
MemChecker to check the validity of the read/written values.

As a bonus, this script also enables the addition of prefetchers, and
the traffic is created to have a mix of random addresses and linear
strides. We use the TaggedPrefetcher since the packets do not have a
request with a PC.

At the moment the code is almost identical to the memtest.py script,
and no effort has been made to factor out the construction of the
tree. The challenge is that the instantiation and connection of the
testers and monitors is done as part of the tree building.

Testing Done

So would this replace memtest.py?  If so, then factoring out the common code would not be an issue.  If not, why not?

Andreas Hansson Feb. 6, 2015, 9:15 a.m. (Feb. 6, 2015, 9:15 a.m.)

The two are complementary:

memtest.py uses MemTest and only tests false sharing, with some progress detection built in

memcheck.py uses TrafficGen and MemCheck and tests actual sharing and prefetching, and has a mix of random and strided access patterns

Steve Reinhardt Feb. 6, 2015, 9:29 a.m. (Feb. 6, 2015, 9:29 a.m.)

But do you expect that there are errors that memtest.py would find that memcheck.py would not, even allowing for some tweaking of the TrafficGen access patterns?  The overhead of not just maintaining but also running two different memory testers seems pretty high, so even if they have complementary approaches, it seems worthwhile only if they have significant non-overlap in their coverage of the memory system state/protocol transition space.

Andreas Hansson Feb. 6, 2015, 9:37 a.m. (Feb. 6, 2015, 9:37 a.m.)

I do believe that they both fill a purpose at the moment.

memtest.py has very little state, and can work on a much larger scale (100's of testers with 10's of cache levels), I have run some 100 trillion cycles with this (once the message-dependent deadlocks are fixes)

memcheck.py relies on the MemCheck tracking of what the allowed read values are, and the state tracking does not scale very well at this point. I believe we can do some more aggressive pruning (and this is planned work), but even running a few billion cycles is currently challenging

Long term the memcheck is probably all we need

Steve Reinhardt Feb. 6, 2015, 10:17 a.m. (Feb. 6, 2015, 10:17 a.m.)

Fair enough, makes sense.  Seems like in the long run memcheck.py could be generalized to plug in MemTest objects in the place of TrafficGen objects, then making the MemCheck objects optional, thus subsuming memtest.py more directly.  I'm fine with leaving that to future work though.

Minor optional comments below...

configs/example/memcheck.py (Diff revision 1)

If you build and populate a SimObjectVector, then assign it to its config hierarchy parent, this problem will take care of itself.

Or you can take the solution used there and copy it, see http://repo.gem5.org/gem5/file/3d17366c0423/src/python/m5/params.py#l269

configs/example/memcheck.py (Diff revision 1)

seems like you don't need this check anymore, right?  might want to leave it in if you agree that memtest.py should be merged in here

Description:

~		Changeset 10692:f0a93f672561
	~	Changeset 10705:bc21bfd38cbd

		config: Add memcheck stress test

		This is a rather unfortunate copy of the memtest.py example script,
		that actually stresses the system with true sharing as opposed to the
		false sharing of the MemTest. To do so it uses TrafficGen instances to
		generate the reads/writes, and MemCheckerMonitor combined with the
		MemChecker to check the validity of the read/written values.

		As a bonus, this script also enables the addition of prefetchers, and
		the traffic is created to have a mix of random addresses and linear
		strides. We use the TaggedPrefetcher since the packets do not have a
		request with a PC.

		At the moment the code is almost identical to the memtest.py script,
		and no effort has been made to factor out the construction of the
		tree. The challenge is that the instantiation and connection of the
		testers and monitors is done as part of the tree building.