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mem: Add additional tolerance to stride prefetcher

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Forces the prefetcher to mispredict twice in a row before resetting the
confidence of prefetching.  This helps cases where a load PC strides by a
constant factor, however it may operate on different arrays at times.
Avoids the cost of retraining.  Primarily helps with small iteration loops.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
This commit is contained in:
Mitch Hayenga 2014-01-29 23:21:26 -06:00
parent 771c864bf4
commit 96317d466e
2 changed files with 11 additions and 4 deletions
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8
src/mem/cache/prefetch/stride.cc vendored
View file

@ -98,12 +98,17 @@ StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
bool stride_match = (new_stride == (*iter)->stride);
if (stride_match && new_stride != 0) {
(*iter)->tolerance = true;
if ((*iter)->confidence < Max_Conf)
(*iter)->confidence++;
} else {
if (!((*iter)->tolerance)) {
(*iter)->stride = new_stride;
if ((*iter)->confidence > Min_Conf)
(*iter)->confidence = 0;
} else {
(*iter)->tolerance = false;
}
}
DPRINTF(HWPrefetch, "hit: PC %x data_addr %x (%s) stride %d (%s), "
@ -118,7 +123,7 @@ StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
return;
for (int d = 1; d <= degree; d++) {
Addr new_addr = data_addr + d * new_stride;
Addr new_addr = data_addr + d * (*iter)->stride;
if (pageStop && !samePage(data_addr, new_addr)) {
// Spanned the page, so now stop
pfSpanPage += degree - d + 1;
@ -160,6 +165,7 @@ StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
new_entry->isSecure = is_secure;
new_entry->stride = 0;
new_entry->confidence = 0;
new_entry->tolerance = false;
tab.push_back(new_entry);
}
}

1
src/mem/cache/prefetch/stride.hh vendored
View file

@ -72,6 +72,7 @@ class StridePrefetcher : public BasePrefetcher
bool isSecure;
int stride;
int confidence;
bool tolerance;
};
std::list<StrideEntry*> table[Max_Contexts];