mem: Allowed tagged instruction prefetching in stride prefetcher

For systems with a tightly coupled L2, a stride-based prefetcher may observe
access requests from both instruction and data L1 caches.  However, the PC
address of an instruction miss gives no relevant training information to the
stride based prefetcher(there is no stride to train).  In theses cases, its
better if the L2 stride prefetcher simply reverted back to a simple N-block
ahead prefetcher.  This patch enables this option.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
This commit is contained in:
Mitch Hayenga 2014-01-29 23:21:26 -06:00
parent 95735e10e7
commit 771c864bf4
3 changed files with 22 additions and 1 deletions

View file

@ -65,6 +65,8 @@ class BasePrefetcher(ClockedObject):
"Only prefetch on read requests (write requests ignored)")
on_prefetch = Param.Bool(True,
"Let lower cache prefetcher train on prefetch requests")
inst_tagged = Param.Bool(True,
"Perform a tagged prefetch for instruction fetches always")
sys = Param.System(Parent.any, "System this device belongs to")
class GHBPrefetcher(BasePrefetcher):

View file

@ -66,6 +66,23 @@ StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
assert(master_id < Max_Contexts);
std::list<StrideEntry*> &tab = table[master_id];
// Revert to simple N-block ahead prefetch for instruction fetches
if (instTagged && pkt->req->isInstFetch()) {
for (int d = 1; d <= degree; d++) {
Addr new_addr = data_addr + d * blkSize;
if (pageStop && !samePage(data_addr, new_addr)) {
// Spanned the page, so now stop
pfSpanPage += degree - d + 1;
return;
}
DPRINTF(HWPrefetch, "queuing prefetch to %x @ %d\n",
new_addr, latency);
addresses.push_back(new_addr);
delays.push_back(latency);
}
return;
}
/* Scan Table for instAddr Match */
std::list<StrideEntry*>::iterator iter;
for (iter = tab.begin(); iter != tab.end(); iter++) {

View file

@ -76,10 +76,12 @@ class StridePrefetcher : public BasePrefetcher
std::list<StrideEntry*> table[Max_Contexts];
bool instTagged;
public:
StridePrefetcher(const Params *p)
: BasePrefetcher(p)
: BasePrefetcher(p), instTagged(p->inst_tagged)
{
}