Tracks if the RAS has been pushed or not during prediction to pop the RAS if neccessary during squash

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Submitter:	Nathanael Premillieu
Repository:	gem5
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Description

I have added a new flag (named pushedRAS) in the PredictorHistory structure. This flag tracks whether the RAS has been pushed or not during a prediction. Then, in the squash function it is used to pop the RAS if necessary.

Testing Done

It has been tested on several of the Spec2006 benchmarks compiled for ARM. For most of the cases, there are less RAS mispredictions.

looks fine to me, but it only seems to impact performance slightly. Did you see bigger gains than a couple %?

Nathanael Premillieu June 19, 2012, 7:13 p.m. (June 19, 2012, 7:13 p.m.)

I have re-run the experiment with the arm_detailed model. There is nearlly no gain (there is even loses for some runs). Now, I wonder why there is so much RAs mispredictions. Is it relalted to the ARM ISA? Because, with the alpha ISA (in an other simulator), I have a lot less RAS mispredictions.

Ali Saidi June 27, 2012, 12:38 a.m. (June 27, 2012, 12:38 a.m.)

I found a bug tagging a pop operation correctly. I couldn't  find it used in some spec2k binaries that I looked at, but apparently some version of compiles do emit them a lot. I'll be pushing it soon.

Change Summary:

English mistake in a comment.

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Revision 2 (+8 -4)

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	src/cpu/o3/bpred_unit.hh
	src/cpu/o3/bpred_unit_impl.hh

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Status: Closed (submitted)