mem: Avoid DRAM write queue iteration for merging and read lookup

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Submitter:	Andreas Hansson
Repository:	gem5
Branch:	default
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Description

Changeset 10889:4e1f65546a25
---------------------------
mem: Avoid DRAM write queue iteration for merging and read lookup

This patch adds a simple lookup structure to avoid iterating over the
write queue to find read matches, and for the merging of write
bursts. Instead of relying on iteration we simply store a set of
currently-buffered write-burst addresses and compare against
these. For the reads we still perform the iteration if we have a
match. For the writes, we rely entirely on the set. Note that there
are corner-cases where sub-bursts would actually not be mergeable
without a read-modify-write. We ignore these cases and opt for speed.

Testing Done

A great simplifictaion. Looks good to me.

src/mem/dram_ctrl.hh (Diff revision 1)

I am guessing that somewhere you make sure that burstSize is a power of two.

Andreas Hansson July 2, 2015, 6:54 a.m. (July 2, 2015, 6:54 a.m.)
```
Yes. I will add a check in the constructor.
```

src/mem/dram_ctrl.cc (Diff revision 1)

Just a thought. Why not add pktCount to this variable after the loop.

Andreas Hansson July 2, 2015, 6:54 a.m. (July 2, 2015, 6:54 a.m.)

Outside the scope of this patch, but indeed something to consider.

src/mem/dram_ctrl.cc (Diff revision 1)

Same thing can be done over here.

Ship It!

Description:

~		Changeset 10818:c9c3503b043a
	~	Changeset 10889:4e1f65546a25

		mem: Avoid DRAM write queue iteration for merging and read lookup

		This patch adds a simple lookup structure to avoid iterating over the
		write queue to find read matches, and for the merging of write
		bursts. Instead of relying on iteration we simply store a set of
		currently-buffered write-burst addresses and compare against
		these. For the reads we still perform the iteration if we have a
		match. For the writes, we rely entirely on the set. Note that there
		are corner-cases where sub-bursts would actually not be mergeable
		without a read-modify-write. We ignore these cases and opt for speed.

Diff:

Revision 2 (+48 -71)

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	src/mem/dram_ctrl.hh
	src/mem/dram_ctrl.cc

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Changeset 10818:c9c3503b043a

Changeset 10889:4e1f65546a25

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Status: Closed (submitted)