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path: root/src/cpu/pred/tournament.hh
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2016-12-21cpu: disallow speculative update of branch predictor tables (o3)Arthur Perais
The Minor and o3 cpu models share the branch prediction code. Minor relies on the BPredUnit::squash() function to update the branch predictor tables on a branch mispre- diction. This is fine because Minor executes in-order, so the update is on the correct path. However, this causes the branch predictor to be updated on out-of-order branch mispredictions when using the o3 model, which should not be the case. This patch guards against speculative update of the branch prediction tables. On a branch misprediction, BPredUnit::squash() calls BpredUnit::update(..., squashed = true). The underlying branch predictor tests against the value of squashed. If it is true, it restores any speculatively updated internal state it might have (e.g., global/local branch history), then returns. If false, it updates its prediction tables. Previously, exist- ing predictors did not test against the "squashed" parameter. To accomodate for this change, the Minor model must now call BPredUnit::squash() then BPredUnit::update(..., squashed = false) on branch mispredictions. Before, calling BpredUnit::squash() performed the prediction tables update. The effect is a slight MPKI improvement when using the o3 model. A further patch should perform the same modifications for the indirect target predictor and BTB (less critical). Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
2016-12-21cpu: correct comments in tournament branch predictorArthur Perais
The tournament predictor is presented as doing speculative update of the global history and non-speculative update of the local history used to generate the branch prediction. However, the code does speculative update of both histories. Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
2016-04-05cpu: Implement per-thread GHRsMitch Hayenga
Branch predictors that use GHRs should index them on a per-thread basis. This makes that so. This is a re-spin of fb51231 after the revert (bd1c6789).
2016-04-05cpu: Add an indirect branch target predictorMitch Hayenga
This patch adds a configurable indirect branch predictor that can be indexed by a combination of GHR and path history hashes. Implements the functionality described in: "Target prediction for indirect jumps" by Chang, Hao, and Patt http://dl.acm.org/citation.cfm?id=264209 This is a re-spin of fb9d142 after the revert (bd1c6789).
2016-04-06Revert power patch sets with unexpected interactionsAndreas Sandberg
The following patches had unexpected interactions with the current upstream code and have been reverted for now: e07fd01651f3: power: Add support for power models 831c7f2f9e39: power: Low-power idle power state for idle CPUs 4f749e00b667: power: Add power states to ClockedObject Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> --HG-- extra : amend_source : 0b6fb073c6bbc24be533ec431eb51fbf1b269508
2016-04-05cpu: Implement per-thread GHRsCurtis Dunham
Branch predictors that use GHRs should index them on a per-thread basis. This makes that so.
2016-04-05cpu: Add an indirect branch target predictorMitch Hayenga
This patch adds a configurable indirect branch predictor that can be indexed by a combination of GHR and path history hashes. Implements the functionality described in: "Target prediction for indirect jumps" by Chang, Hao, and Patt http://dl.acm.org/citation.cfm?id=264209
2015-09-15cpu: pred: Local Predictor Reset in Tournament PredictorAndrew Lukefahr
When a branch gets squashed, it's speculative branch predictor state should get rolled back in squash(). However, only the globalHistory state was being rolled back. This patch adds (at least some) support for rolling back the local predictor state also. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2015-04-13cpu: re-organizes the branch predictor structure.Dibakar Gope
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2014-09-03cpu: Fix incorrect speculative branch predictor behaviorMitch Hayenga
When a branch mispredicted gem5 would squash all history after and including the mispredicted branch. However, the mispredicted branch is still speculative and its history is required to rollback state if another, older, branch mispredicts. This leads to things like RAS corruption.
2013-01-24branch predictor: move out of o3 and inorder cpusNilay Vaish ext:(%2C%20Timothy%20Jones%20%3Ctimothy.jones%40cl.cam.ac.uk%3E)
This patch moves the branch predictor files in the o3 and inorder directories to src/cpu/pred. This allows sharing the branch predictor across different cpu models. This patch was originally posted by Timothy Jones in July 2010 but never made it to the repository. --HG-- rename : src/cpu/o3/bpred_unit.cc => src/cpu/pred/bpred_unit.cc rename : src/cpu/o3/bpred_unit.hh => src/cpu/pred/bpred_unit.hh rename : src/cpu/o3/bpred_unit_impl.hh => src/cpu/pred/bpred_unit_impl.hh rename : src/cpu/o3/sat_counter.hh => src/cpu/pred/sat_counter.hh
2012-12-06TournamentBP: Fix some bugs with table sizes and countersErik Tomusk
globalHistoryBits, globalPredictorSize, and choicePredictorSize are decoupled. globalHistoryBits controls how much history is kept, global and choice predictor sizes control how much of that history is used when accessing predictor tables. This way, global and choice predictors can actually be different sizes, and it is no longer possible to walk off the predictor arrays and cause a seg fault. There are now individual thresholds for choice, global, and local saturating counters, so that taken/not taken decisions are correct even when the predictors' counters' sizes are different. The interface for localPredictorSize has been removed from TournamentBP because the value can be calculated from localHistoryBits. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2012-02-13BP: Fix several Branch Predictor issues.Mrinmoy Ghosh
1. Updates the Branch Predictor correctly to the state just after a mispredicted branch, if a squash occurs. 2. If a BTB does not find an entry, the branch is predicted not taken. The global history is modified to correctly reflect this prediction. 3. Local history is now updated at the fetch stage instead of execute stage. 4. In the Update stage of the branch predictor the local predictors are now correctly updated according to the state of local history during fetch stage. This patch also improves performance by as much as 17% on some benchmarks
2009-06-04move: put predictor includes and cc files into the same placeNathan Binkert
--HG-- rename : src/cpu/2bit_local_pred.cc => src/cpu/pred/2bit_local.cc rename : src/cpu/o3/2bit_local_pred.hh => src/cpu/pred/2bit_local.hh rename : src/cpu/btb.cc => src/cpu/pred/btb.cc rename : src/cpu/o3/btb.hh => src/cpu/pred/btb.hh rename : src/cpu/ras.cc => src/cpu/pred/ras.cc rename : src/cpu/o3/ras.hh => src/cpu/pred/ras.hh rename : src/cpu/tournament_pred.cc => src/cpu/pred/tournament.cc rename : src/cpu/o3/tournament_pred.hh => src/cpu/pred/tournament.hh