Information
Submitter:	Chang Hyun Park
Repository:	gem5
Branch:
Bugs:
Depends On:
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Description

Changing SnoopMask type from `uint64_t` to `std::bitset`

This allows the size of the system (core count) to be larger than the current system.
The # of slave ports was 2xcore + 1 for a basic example/se.py simulation with --caches option.
Thus the maximum core size when using SnoopFilter was 31 due to the 64 bit type.
Bitset allows this to be expanded, allowing the use of SnoopFilter to be used in larger core count systems.

TODO: Dynamically allow the build system to specify the MAX_CORES macro value.

Testing Done

Testing done on config file example/se.py with --caches option.

(Modified code to add the SnoopFilter() into the SystemXBar)

Change Summary:

Changed title

Summary:

-	Changing SnoopMask type from uint64_t to std::bitset
+	SnoopFilter: Changing SnoopMask type from uint64_t to std::bitset

Description:

		Changing SnoopMask type from uint64_t to std::bitset
~		This allows the size of the system to be larger than the current system.
	~	This allows the size of the system (core count) to be larger than the current system.
		The # of slave ports was 2xcore + 1 for a basic example/se.py simulation with --caches option.
		Thus the maximum core size was 31 due to the 64 bit type.
		Bitset allows this to be expanded, allowing the use of snoop filter to be used in larger core count systems.

		TODO: Dynamically allow the build system to specify the MAX_CORES macro value.

Description:

~		Changing SnoopMask type from uint64_t to std::bitset
	~	Changing SnoopMask type from `uint64_t` to `std::bitset`
-		This allows the size of the system (core count) to be larger than the current system.
-		The # of slave ports was 2xcore + 1 for a basic example/se.py simulation with --caches option.
-		Thus the maximum core size was 31 due to the 64 bit type.
-		Bitset allows this to be expanded, allowing the use of snoop filter to be used in larger core count systems.

~		TODO: Dynamically allow the build system to specify the MAX_CORES macro value.
	~	This allows the size of the system (core count) to be larger than the current system.
	+	The # of slave ports was 2xcore + 1 for a basic `example/se.py` simulation with `--caches` option.
	+	Thus the maximum core size when using SnoopFilter was 31 due to the 64 bit type.
	+	Bitset allows this to be expanded, allowing the use of SnoopFilter to be used in larger core count systems.
	+
	+	TODO: Dynamically allow the build system to specify the `MAX_CORES` macro value.

Testing Done:

	+	Testing done on config file `example/se.py` with `--caches option`.
	+	(Modified code to add the `SnoopFilter()` into the `SystemXBar`)

Commit:

-	581cda593719
+	b8de61e29ce1

Diff:

Revision 2 (+26 -13)

Show changes

	src/mem/snoop_filter.hh
	src/mem/snoop_filter.cc

Thanks for the patch.

I am wondering if this is really the way to go. I would argue that one enormous crossbar is not realistic for 32+ cores, and if you would create this as a number of clusters the problem should go away. Have you considered that?

Thus, you place 4-8 cores in a cluster, with their own ClusterXBar. This crossbar is then connected to the SystemXBar. By doing this the ClusterXBar should only see 16 ports and the total system could still accommodate 16 * 16 cores or more.

Andreas Hansson Aug. 3, 2015, 2:17 p.m. (Aug. 3, 2015, 2:17 p.m.)

Any comments? I am about to post some patches for the snoop filter, and as a follow up we could easily make the snoop mask "dense" in that it would only track snooping ports. That would allow you the 32+ cores for a single-hop crossbar, as mentioned above. Would that be enough?

Chang Hyun Park Aug. 3, 2015, 5:43 p.m. (Aug. 3, 2015, 5:43 p.m.)

Sorry for the late reply, I haven't been able to work on gem5 since my patch, and so I don't think I'll be able to work on the clustered crossbar.

Andreas Hansson Aug. 4, 2015, 12:15 a.m. (Aug. 4, 2015, 12:15 a.m.)

No worries. I hope you are able to review the snoop filter patches. I hope to post them next week.

You have a pending review.

Review Board 2.0.15

This change has been discarded.

SnoopFilter: Changing SnoopMask type from uint64_t to std::bitset

Changing SnoopMask type from `uint64_t` to `std::bitset`

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Change Summary:

Summary:

Description:

Description:

Changing SnoopMask type from `uint64_t` to `std::bitset`

Testing Done:

Commit:

Diff:

Status: Discarded