From b6203360ef684a8dc32981221336f5d216ce2668 Mon Sep 17 00:00:00 2001
From: Ali Saidi <Ali.Saidi@ARM.com>
Date: Fri, 19 Aug 2011 15:08:07 -0500
Subject: LSQ: Set store predictor to periodically clear itself as recommended
 in the storesets paper.

This patch improves performance by as much as 10% on some spec benchmarks.
---
 src/cpu/o3/store_set.cc | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

(limited to 'src/cpu/o3/store_set.cc')

diff --git a/src/cpu/o3/store_set.cc b/src/cpu/o3/store_set.cc
index fc87c417e..acd4a8d0a 100644
--- a/src/cpu/o3/store_set.cc
+++ b/src/cpu/o3/store_set.cc
@@ -34,8 +34,8 @@
 #include "cpu/o3/store_set.hh"
 #include "debug/StoreSet.hh"
 
-StoreSet::StoreSet(int _SSIT_size, int _LFST_size)
-    : SSITSize(_SSIT_size), LFSTSize(_LFST_size)
+StoreSet::StoreSet(uint64_t clear_period, int _SSIT_size, int _LFST_size)
+    : clearPeriod(clear_period), SSITSize(_SSIT_size), LFSTSize(_LFST_size)
 {
     DPRINTF(StoreSet, "StoreSet: Creating store set object.\n");
     DPRINTF(StoreSet, "StoreSet: SSIT size: %i, LFST size: %i.\n",
@@ -68,6 +68,8 @@ StoreSet::StoreSet(int _SSIT_size, int _LFST_size)
     indexMask = SSITSize - 1;
 
     offsetBits = 2;
+
+    memOpsPred = 0;
 }
 
 StoreSet::~StoreSet()
@@ -75,10 +77,11 @@ StoreSet::~StoreSet()
 }
 
 void
-StoreSet::init(int _SSIT_size, int _LFST_size)
+StoreSet::init(uint64_t clear_period, int _SSIT_size, int _LFST_size)
 {
     SSITSize = _SSIT_size;
     LFSTSize = _LFST_size;
+    clearPeriod = clear_period;
 
     DPRINTF(StoreSet, "StoreSet: Creating store set object.\n");
     DPRINTF(StoreSet, "StoreSet: SSIT size: %i, LFST size: %i.\n",
@@ -103,6 +106,8 @@ StoreSet::init(int _SSIT_size, int _LFST_size)
     indexMask = SSITSize - 1;
 
     offsetBits = 2;
+
+    memOpsPred = 0;
 }
 
 
@@ -179,9 +184,22 @@ StoreSet::violation(Addr store_PC, Addr load_PC)
     }
 }
 
+void
+StoreSet::checkClear()
+{
+    memOpsPred++;
+    if (memOpsPred > clearPeriod) {
+        DPRINTF(StoreSet, "Wiping predictor state beacuse %d ld/st executed\n",
+                clearPeriod);
+        memOpsPred = 0;
+        clear();
+    }
+}
+
 void
 StoreSet::insertLoad(Addr load_PC, InstSeqNum load_seq_num)
 {
+    checkClear();
     // Does nothing.
     return;
 }
@@ -193,6 +211,7 @@ StoreSet::insertStore(Addr store_PC, InstSeqNum store_seq_num, ThreadID tid)
 
     int store_SSID;
 
+    checkClear();
     assert(index < SSITSize);
 
     if (!validSSIT[index]) {
-- 
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