Juan Manuel Cebrián González has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/28053 )
Change subject: mem-ruby: Fix for ruby latency
......................................................................
mem-ruby: Fix for ruby latency
The classic memory model clears L1 hits instantaneously and sets the 'when'
to curTick + hit_latency. Ruby models however advance the curTick instead.
Therefore the legacy '+1' adds an additional cycle to ruby L1 cache hits.
This causes significantly more front-end stalls of the o3 cpu when compared
to real Intel hardware. By applying this fix both performance and
simulation time are improved by around 30%. Front-end stalls look much
closer to real hardware with this fix.
Change-Id: I4c91dc09bff5f45f1d1e42edc13d3c15d6205c46
---
M src/mem/packet_queue.cc
M src/mem/packet_queue.hh
M src/mem/request.hh
M src/mem/ruby/system/Sequencer.cc
4 files changed, 34 insertions(+), 3 deletions(-)
diff --git a/src/mem/packet_queue.cc b/src/mem/packet_queue.cc
index dd1ba3d..60b1889 100644
--- a/src/mem/packet_queue.cc
+++ b/src/mem/packet_queue.cc
@@ -148,12 +148,18 @@
// either the packet list is empty or this has to be inserted
// before every other packet
transmitList.emplace_front(when, pkt);
- schedSendEvent(when);
+ schedSendEvent(when,pkt);
}
void
PacketQueue::schedSendEvent(Tick when)
{
+ schedSendEvent(when,NULL);
+}
+
+void
+PacketQueue::schedSendEvent(Tick when, PacketPtr pkt)
+{
// if we are waiting on a retry just hold off
if (waitingOnRetry) {
DPRINTF(PacketQueue, "Not scheduling send as waiting for retry\n");
@@ -162,10 +168,20 @@
}
if (when != MaxTick) {
+ // The classic memory model clears L1 hits instantaneously and
+ // sets the 'when' to curTick + hit_latency. Ruby models however
+ // advance the curTick instead. Therefore the legacy '+1' adds an
+ // additional cycle to ruby L1 cache hits.
// we cannot go back in time, and to be consistent we stick to
// one tick in the future
- when = std::max(when, curTick() + 1);
+ Tick initWhen = when;
+ when = std::max(initWhen, curTick() + 1);
// @todo Revisit the +1
+ if (pkt != NULL) {
+ if (pkt->req->wasHandledByRuby()) {
+ when = std::max(initWhen, curTick());
+ }
+ }
if (!sendEvent.scheduled()) {
em.schedule(&sendEvent, when);
diff --git a/src/mem/packet_queue.hh b/src/mem/packet_queue.hh
index b9c5b75..bac4db2 100644
--- a/src/mem/packet_queue.hh
+++ b/src/mem/packet_queue.hh
@@ -194,6 +194,12 @@
*
* @param when time to schedule an event
*/
+ void schedSendEvent(Tick when, PacketPtr pkt);
+
+ /**
+ * Wrapper for old schedSendEvent
+ * @param when time to schedule an event
+ */
void schedSendEvent(Tick when);
/**
diff --git a/src/mem/request.hh b/src/mem/request.hh
index aca9fe8..b127a4a 100644
--- a/src/mem/request.hh
+++ b/src/mem/request.hh
@@ -251,6 +251,9 @@
ARG_SEGMENT = 0x00000800,
};
+ /* Flag set when a packet passes through Ruby */
+ bool handledByRuby;
+
private:
typedef uint16_t PrivateFlagsType;
typedef ::Flags<PrivateFlagsType> PrivateFlags;
@@ -299,6 +302,7 @@
privateFlags.set(VALID_PADDR|VALID_SIZE);
depth = 0;
accessDelta = 0;
+ handledByRuby = false;
//translateDelta = 0;
}
@@ -399,7 +403,7 @@
_extraData(0), _contextId(0), _pc(0),
_reqInstSeqNum(0), atomicOpFunctor(nullptr), translateDelta(0),
accessDelta(0), depth(0)
- {}
+ { handledByRuby = false; }
Request(Addr paddr, unsigned size, Flags flags, MasterID mid,
InstSeqNum seq_num, ContextID cid)
@@ -540,6 +544,7 @@
accessDelta = 0;
translateDelta = 0;
atomicOpFunctor = std::move(amo_op);
+ handledByRuby = false;
}
/**
@@ -908,6 +913,8 @@
bool isAtomicReturn() const { return _flags.isSet(ATOMIC_RETURN_OP); }
bool isAtomicNoReturn() const { return
_flags.isSet(ATOMIC_NO_RETURN_OP); }
+ bool wasHandledByRuby() const { return handledByRuby; };
+
bool
isAtomic() const
{
diff --git a/src/mem/ruby/system/Sequencer.cc
b/src/mem/ruby/system/Sequencer.cc
index a90523e..4f1ba2a 100644
--- a/src/mem/ruby/system/Sequencer.cc
+++ b/src/mem/ruby/system/Sequencer.cc
@@ -520,6 +520,8 @@
return RequestStatus_BufferFull;
}
+ pkt->req->handledByRuby = true;
+
RubyRequestType primary_type = RubyRequestType_NULL;
RubyRequestType secondary_type = RubyRequestType_NULL;
--
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Gerrit-Project: public/gem5
Gerrit-Branch: master
Gerrit-Change-Id: I4c91dc09bff5f45f1d1e42edc13d3c15d6205c46
Gerrit-Change-Number: 28053
Gerrit-PatchSet: 1
Gerrit-Owner: Juan Manuel Cebrián González <jm.cebriangonza...@gmail.com>
Gerrit-MessageType: newchange
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