mem-cache: implement a probe-based interface

The HW Prefetcher of a cache can now listen events
from their associated CPUs and from its own cache.

Change-Id: I28aecd8faf8ed44be94464d84485bd1cea2efae3
Reviewed-on: https://gem5-review.googlesource.com/c/14155
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/prefetch/Prefetcher.py

@@ -40,13 +40,29 @@
 #          Mitch Hayenga
 
 from ClockedObject import ClockedObject
+from m5.SimObject import *
 from m5.params import *
 from m5.proxy import *
 
+class HWPProbeEvent(object):
+    def __init__(self, prefetcher, obj, *listOfNames):
+        self.obj = obj
+        self.prefetcher = prefetcher
+        self.names = listOfNames
+
+    def register(self):
+        if self.obj:
+            for name in self.names:
+                self.prefetcher.getCCObject().addEventProbe(
+                    self.obj.getCCObject(), name)
+
 class BasePrefetcher(ClockedObject):
     type = 'BasePrefetcher'
     abstract = True
     cxx_header = "mem/cache/prefetch/base.hh"
+    cxx_exports = [
+        PyBindMethod("addEventProbe"),
+    ]
     sys = Param.System(Parent.any, "System this prefetcher belongs to")
 
     on_miss = Param.Bool(False, "Only notify prefetcher on misses")
@@ -54,6 +70,26 @@ class BasePrefetcher(ClockedObject):
     on_write = Param.Bool(True, "Notify prefetcher on writes")
     on_data  = Param.Bool(True, "Notify prefetcher on data accesses")
     on_inst  = Param.Bool(True, "Notify prefetcher on instruction accesses")
+    prefetch_on_access = Param.Bool(Parent.prefetch_on_access,
+        "Notify the hardware prefetcher on every access (not just misses)")
+
+    _events = []
+    def addEvent(self, newObject):
+        self._events.append(newObject)
+
+    # Override the normal SimObject::regProbeListeners method and
+    # register deferred event handlers.
+    def regProbeListeners(self):
+        for event in self._events:
+           event.register()
+        self.getCCObject().regProbeListeners()
+
+    def listenFromProbe(self, simObj, *probeNames):
+        if not isinstance(simObj, SimObject):
+            raise TypeError("argument must be of SimObject type")
+        if len(probeNames) <= 0:
+            raise TypeError("probeNames must have at least one element")
+        self.addEvent(HWPProbeEvent(self, simObj, *probeNames))
 
 class QueuedPrefetcher(BasePrefetcher):
     type = "QueuedPrefetcher"

src/mem/cache/prefetch/base.cc

@@ -51,16 +51,24 @@
 #include <cassert>
 
 #include "base/intmath.hh"
+#include "cpu/base.hh"
 #include "mem/cache/base.hh"
 #include "params/BasePrefetcher.hh"
 #include "sim/system.hh"
 
+void
+BasePrefetcher::PrefetchListener::notify(const PacketPtr &pkt)
+{
+    parent.probeNotify(pkt);
+}
+
 BasePrefetcher::BasePrefetcher(const BasePrefetcherParams *p)
-    : ClockedObject(p), cache(nullptr), blkSize(0), lBlkSize(0),
+    : ClockedObject(p), listeners(), cache(nullptr), blkSize(0), lBlkSize(0),
       system(p->sys), onMiss(p->on_miss), onRead(p->on_read),
       onWrite(p->on_write), onData(p->on_data), onInst(p->on_inst),
       masterId(system->getMasterId(this)),
-      pageBytes(system->getPageBytes())
+      pageBytes(system->getPageBytes()),
+      prefetchOnAccess(p->prefetch_on_access)
 {
 }
 
@@ -163,3 +171,38 @@ BasePrefetcher::pageIthBlockAddress(Addr page, uint32_t blockIndex) const
 {
     return page + (blockIndex << lBlkSize);
 }
+
+void
+BasePrefetcher::probeNotify(const PacketPtr &pkt)
+{
+    // Don't notify prefetcher on SWPrefetch, cache maintenance
+    // operations or for writes that we are coaslescing.
+    if (pkt->cmd.isSWPrefetch()) return;
+    if (pkt->req->isCacheMaintenance()) return;
+    if (pkt->isWrite() && cache != nullptr && cache->coalesce()) return;
+    notify(pkt);
+}
+
+void
+BasePrefetcher::regProbeListeners()
+{
+    /**
+     * If no probes were added by the configuration scripts, connect to the
+     * parent cache using the probe "Miss". Also connect to "Hit", if the
+     * cache is configured to prefetch on accesses.
+     */
+    if (listeners.empty() && cache != nullptr) {
+        ProbeManager *pm(cache->getProbeManager());
+        listeners.push_back(new PrefetchListener(*this, pm, "Miss"));
+        if (prefetchOnAccess) {
+            listeners.push_back(new PrefetchListener(*this, pm, "Hit"));
+        }
+    }
+}
+
+void
+BasePrefetcher::addEventProbe(SimObject *obj, const char *name)
+{
+    ProbeManager *pm(obj->getProbeManager());
+    listeners.push_back(new PrefetchListener(*this, pm, name));
+}

src/mem/cache/prefetch/base.hh

@@ -56,6 +56,7 @@
 #include "mem/packet.hh"
 #include "mem/request.hh"
 #include "sim/clocked_object.hh"
+#include "sim/probe/probe.hh"
 
 class BaseCache;
 struct BasePrefetcherParams;
@@ -63,6 +64,19 @@ class System;
 
 class BasePrefetcher : public ClockedObject
 {
+    class PrefetchListener : public ProbeListenerArgBase<PacketPtr>
+    {
+      public:
+        PrefetchListener(BasePrefetcher &_parent, ProbeManager *pm,
+                         const std::string &name)
+            : ProbeListenerArgBase(pm, name),
+              parent(_parent) {}
+        void notify(const PacketPtr &pkt) override;
+      protected:
+        BasePrefetcher &parent;
+    };
+
+    std::vector<PrefetchListener *> listeners;
   protected:
 
     // PARAMETERS
@@ -99,6 +113,9 @@ class BasePrefetcher : public ClockedObject
 
     const Addr pageBytes;
 
+    /** Prefetch on every access, not just misses */
+    const bool prefetchOnAccess;
+
     /** Determine if this access should be observed */
     bool observeAccess(const PacketPtr &pkt) const;
 
@@ -135,14 +152,31 @@ class BasePrefetcher : public ClockedObject
     /**
      * Notify prefetcher of cache access (may be any access or just
      * misses, depending on cache parameters.)
-     * @retval Time of next prefetch availability, or MaxTick if none.
      */
-    virtual Tick notify(const PacketPtr &pkt) = 0;
+    virtual void notify(const PacketPtr &pkt) = 0;
 
     virtual PacketPtr getPacket() = 0;
 
     virtual Tick nextPrefetchReadyTime() const = 0;
 
     virtual void regStats();
+
+    /**
+     * Register probe points for this object.
+     */
+    void regProbeListeners() override;
+
+    /**
+     * Process a notification event from the ProbeListener.
+     * @param pkt The memory request causing the event
+     */
+    void probeNotify(const PacketPtr &pkt);
+
+    /**
+     * Add a SimObject and a probe name to listen events from
+     * @param obj The SimObject pointer to listen from
+     * @param name The probe name
+     */
+    void addEventProbe(SimObject *obj, const char *name);
 };
 #endif //__MEM_CACHE_PREFETCH_BASE_HH__

src/mem/cache/prefetch/queued.cc

@@ -63,7 +63,7 @@ QueuedPrefetcher::~QueuedPrefetcher()
     }
 }
 
-Tick
+void
 QueuedPrefetcher::notify(const PacketPtr &pkt)
 {
     // Verify this access type is observed by prefetcher
@@ -110,8 +110,6 @@ QueuedPrefetcher::notify(const PacketPtr &pkt)
             }
         }
     }
-
-    return pfq.empty() ? MaxTick : pfq.front().tick;
 }
 
 PacketPtr

src/mem/cache/prefetch/queued.hh

@@ -115,7 +115,7 @@ class QueuedPrefetcher : public BasePrefetcher
     QueuedPrefetcher(const QueuedPrefetcherParams *p);
     virtual ~QueuedPrefetcher();
 
-    Tick notify(const PacketPtr &pkt);
+    void notify(const PacketPtr &pkt) override;
     PacketPtr insert(AddrPriority& info, bool is_secure);
 
     // Note: This should really be pure virtual, but doesnt go well with params