MESI: Add queues for stalled requests

Information
Submitter:	Nilay Vaish
Repository:	gem5
Branch:	default
Bugs:
Depends On:
Reviewers
Groups:	Default
People:

Description

Changeset 8819:aab2b174328e
---------------------------
MESI: Add queues for stalled requests
This patch adds the stall and wait on the mandatory queue of L1 cache
controller of the MESI CMP directory protocol. The changes have been
tested for a million loads with 16 and 32 processors. 16 different
seeds for bith 16 and 32 processor systems.

Testing Done

Do you have to always call wakeUpAllDependents?  Initially it atleast was my hope that the per cache block wakeUpDependents would be sufficient.  However, I could see that in certain situations where requets are stalled because a tbe entry is unavailable that the per address wakeUpDependents could lead to starvation.  Do you think we should just elimiate wakeUpDependents and just use wakeUpAllDependents?

Nilay Vaish March 3, 2011, 9:14 a.m. (March 3, 2011, 9:14 a.m.)

Brad, I also thought that stalling on cache block basis should be sufficient. In 
fact my initial code used wakeUpDependents() only. But that did not work out, and 
I was not able to figure out why that might be the case. And then I thought that 
stalling requests on a particular address might not be correct. Let me pose this 
question to you, is stalling on an address same as stalling on a cache block? If it 
is, then certainly I do not see the need for wakeUpAllDependents(), at least not in 
the MESI L1 cache controller. But in case the two are not same, then I think we would 
need to wake up all requests whenever there is a transition from a transient to a 
stable state.

Summary:

-	Ruby: Add stall and wait to MESI CMP directory
+	MESI: Add queues for stalled requests

Description:

~		This patch adds the stall and wait on the mandatory queue of L1 cache
~		controller of the MESI CMP directory protocol. It is intended to be
~		more of a discussion (so as to improve my understanding).
	~	Changeset 8819:aab2b174328e
	~
	~	MESI: Add queues for stalled requests
	+	This patch adds the stall and wait on the mandatory queue of L1 cache
	+	controller of the MESI CMP directory protocol. The changes have been
	+	tested for a million loads with 16 and 32 processors. 16 different
	+	seeds for bith 16 and 32 processor systems.

Branch:

+	default

Diff:

Revision 3 (+66 -38)

Show changes

	src/mem/protocol/MESI_CMP_directory-L1cache.sm
	src/mem/protocol/MESI_CMP_directory-L2cache.sm
	src/mem/protocol/MESI_CMP_directory-dir.sm

Testing Done:

-		The changes have been tested for 16 processors for 40 different random
-		seeds with number of loads varying from a 1,000,000 - 4,000,000. The only
-		concern is that I had to change the dead lock threshold in RubyTester.py
-		which is surprising.

You have a pending review.

Review Board 2.0.15

This change has been marked as submitted.

Screenshots

Files

Summary:

Description:

Changeset 8819:aab2b174328e

Branch:

Diff:

Testing Done:

Status: Closed (submitted)