mem-cache: Use CircularQueue for the STeMS's RMOB
Replace rmobHead functionality with a CircularQueue. As a side
effect, RMOB entry's valid bit was removed.
Change-Id: If0b39cfe15de1e47dde0689a0ebc46b623ec1e55
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24539
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Javier Bueno Hedo <javier.bueno@metempsy.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/mem/cache/prefetch/spatio_temporal_memory_streaming.cc b/src/mem/cache/prefetch/spatio_temporal_memory_streaming.cc
index 932c7f6..dd15012 100644
--- a/src/mem/cache/prefetch/spatio_temporal_memory_streaming.cc
+++ b/src/mem/cache/prefetch/spatio_temporal_memory_streaming.cc
@@ -50,7 +50,7 @@
p->pattern_sequence_table_replacement_policy,
ActiveGenerationTableEntry(
spatialRegionSize / blkSize)),
- rmob(p->region_miss_order_buffer_entries), rmobHead(0)
+ rmob(p->region_miss_order_buffer_entries)
{
fatal_if(!isPowerOf2(spatialRegionSize),
"The spatial region size must be a power of 2.");
@@ -106,13 +106,12 @@
void
STeMS::addToRMOB(Addr sr_addr, Addr pst_addr, unsigned int delta)
{
- RegionMissOrderBufferEntry &rmob_entry = rmob[rmobHead];
- rmobHead = (rmobHead + 1) % rmob.size();
-
+ RegionMissOrderBufferEntry rmob_entry;
rmob_entry.srAddress = sr_addr;
rmob_entry.pstAddress = pst_addr;
rmob_entry.delta = delta;
- rmob_entry.valid = true;
+
+ rmob.push_back(rmob_entry);
}
void
@@ -171,13 +170,12 @@
// Prefetch generation: if this is a miss, search for the most recent
// entry in the RMOB, and reconstruct the registered access sequence
if (pfi.isCacheMiss()) {
- for (unsigned int idx = (rmobHead - 1) % rmob.size();
- idx != rmobHead && rmob[idx].valid;
- idx = (idx - 1) % rmob.size())
- {
- if (rmob[idx].srAddress == sr_addr) {
+ auto it = rmob.end();
+ while (it != rmob.begin()) {
+ --it;
+ if (it->srAddress == sr_addr) {
// reconstruct the access sequence
- reconstructSequence(idx, addresses);
+ reconstructSequence(it, addresses);
break;
}
}
@@ -185,37 +183,34 @@
}
void
-STeMS::reconstructSequence(unsigned int rmob_idx,
+STeMS::reconstructSequence(
+ CircularQueue<RegionMissOrderBufferEntry>::iterator rmob_it,
std::vector<AddrPriority> &addresses)
{
std::vector<Addr> reconstruction(reconstructionEntries, MaxAddr);
unsigned int idx = 0;
- // process rmob entries from rmob_idx (most recent with
- // address = sr_addr) to the last one (rmobHead)
- for (int i = rmob_idx;
- i != rmobHead && idx < reconstructionEntries;
- i = (i + 1) % rmob.size())
- {
- reconstruction[idx] = rmob[i].srAddress * spatialRegionSize;
- unsigned int next_i = (i + 1) % rmob.size();
- idx += rmob[next_i].delta + 1;
+
+ // Process rmob entries from rmob_it (most recent with address = sr_addr)
+ // to the latest one
+ for (auto it = rmob_it; it != rmob.end() && (idx < reconstructionEntries);
+ it++) {
+ reconstruction[idx] = it->srAddress * spatialRegionSize;
+ idx += (it+1)->delta + 1;
}
+
// Now query the PST with the PC of each RMOB entry
idx = 0;
- for (int i = rmob_idx;
- i != rmobHead && idx < reconstructionEntries;
- i = (i + 1) % rmob.size())
- {
+ for (auto it = rmob_it; it != rmob.end() && (idx < reconstructionEntries);
+ it++) {
ActiveGenerationTableEntry *pst_entry =
- patternSequenceTable.findEntry(rmob[i].pstAddress,
- false /* unused */);
+ patternSequenceTable.findEntry(it->pstAddress, false /* unused */);
if (pst_entry != nullptr) {
patternSequenceTable.accessEntry(pst_entry);
for (auto &seq_entry : pst_entry->sequence) {
if (seq_entry.counter > 1) {
// 2-bit counter: high enough confidence with a
// value greater than 1
- Addr rec_addr = rmob[i].srAddress * spatialRegionSize +
+ Addr rec_addr = it->srAddress * spatialRegionSize +
seq_entry.offset;
unsigned ridx = idx + seq_entry.delta;
// Try to use the corresponding position, if it has been
@@ -241,9 +236,9 @@
}
}
}
- unsigned int next_i = (i + 1) % rmob.size();
- idx += rmob[next_i].delta + 1;
+ idx += (it+1)->delta + 1;
}
+
for (Addr pf_addr : reconstruction) {
if (pf_addr != MaxAddr) {
addresses.push_back(AddrPriority(pf_addr, 0));
diff --git a/src/mem/cache/prefetch/spatio_temporal_memory_streaming.hh b/src/mem/cache/prefetch/spatio_temporal_memory_streaming.hh
index 8f8704a..4e0ca28 100644
--- a/src/mem/cache/prefetch/spatio_temporal_memory_streaming.hh
+++ b/src/mem/cache/prefetch/spatio_temporal_memory_streaming.hh
@@ -43,6 +43,7 @@
#include <vector>
+#include "base/circular_queue.hh"
#include "base/sat_counter.hh"
#include "mem/cache/prefetch/associative_set.hh"
#include "mem/cache/prefetch/queued.hh"
@@ -161,14 +162,10 @@
Addr pstAddress;
/** Delta within the global miss order sequence */
unsigned int delta;
- /** Valid bit */
- bool valid;
};
/** Region Miss Order Buffer (RMOB) */
- std::vector<RegionMissOrderBufferEntry> rmob;
- /** First free position (or older, if it is full) of the RMOB */
- unsigned int rmobHead;
+ CircularQueue<RegionMissOrderBufferEntry> rmob;
/** Counter to keep the count of accesses between trigger accesses */
unsigned int lastTriggerCounter;
@@ -186,11 +183,14 @@
/**
* Reconstructs a sequence of accesses and generates the prefetch
* addresses, adding them to the addresses vector
- * @param rmob_idx rmob position to start generating from
+ *
+ * @param rmob_it rmob position to start generating from.
* @param addresses vector to add the addresses to be prefetched
*/
- void reconstructSequence(unsigned int rmob_idx,
- std::vector<AddrPriority> &addresses);
+ void reconstructSequence(
+ CircularQueue<RegionMissOrderBufferEntry>::iterator rmob_it,
+ std::vector<AddrPriority> &addresses);
+
public:
STeMS(const STeMSPrefetcherParams* p);
~STeMS() = default;
