/*
* Copyright (c) 2012-2013, 2015-2018 ARM Limited
* All rights reserved.
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2002-2005 The Regents of The University of Michigan
* Copyright (c) 2010 Advanced Micro Devices, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Erik Hallnor
* Dave Greene
*/
/**
* @file
* Miss Status and Handling Register (MSHR) definitions.
*/
#include "mem/cache/mshr.hh"
#include <algorithm>
#include <cassert>
#include <string>
#include <vector>
#include "base/logging.hh"
#include "base/types.hh"
#include "debug/Cache.hh"
#include "mem/cache/cache.hh"
#include "sim/core.hh"
using namespace std;
MSHR::MSHR() : downstreamPending(false),
pendingModified(false),
postInvalidate(false), postDowngrade(false),
isForward(false)
{
}
MSHR::TargetList::TargetList()
: needsWritable(false), hasUpgrade(false), allocOnFill(false)
{}
void
MSHR::TargetList::updateFlags(PacketPtr pkt, Target::Source source,
bool alloc_on_fill)
{
if (source != Target::FromSnoop) {
if (pkt->needsWritable()) {
needsWritable = true;
}
// StoreCondReq is effectively an upgrade if it's in an MSHR
// since it would have been failed already if we didn't have a
// read-only copy
if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
hasUpgrade = true;
}
// potentially re-evaluate whether we should allocate on a fill or
// not
allocOnFill = allocOnFill || alloc_on_fill;
}
}
void
MSHR::TargetList::populateFlags()
{
resetFlags();
for (auto& t: *this) {
updateFlags(t.pkt, t.source, t.allocOnFill);
}
}
inline void
MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
Counter order, Target::Source source, bool markPending,
bool alloc_on_fill)
{
updateFlags(pkt, source, alloc_on_fill);
if (markPending) {
// Iterate over the SenderState stack and see if we find
// an MSHR entry. If we do, set the downstreamPending
// flag. Otherwise, do nothing.
MSHR *mshr = pkt->findNextSenderState<MSHR>();
if (mshr != nullptr) {
assert(!mshr->downstreamPending);
mshr->downstreamPending = true;
} else {
// No need to clear downstreamPending later
markPending = false;
}
}
emplace_back(pkt, readyTime, order, source, markPending, alloc_on_fill);
}
static void
replaceUpgrade(PacketPtr pkt)
{
// remember if the current packet has data allocated
bool has_data = pkt->hasData() || pkt->hasRespData();
if (pkt->cmd == MemCmd::UpgradeReq) {
pkt->cmd = MemCmd::ReadExReq;
DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
} else if (pkt->cmd == MemCmd::SCUpgradeReq) {
pkt->cmd = MemCmd::SCUpgradeFailReq;
DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
} else if (pkt->cmd == MemCmd::StoreCondReq) {
pkt->cmd = MemCmd::StoreCondFailReq;
DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
}
if (!has_data) {
// there is no sensible way of setting the data field if the
// new command actually would carry data
assert(!pkt->hasData());
if (pkt->hasRespData()) {
// we went from a packet that had no data (neither request,
// nor response), to one that does, and therefore we need to
// actually allocate space for the data payload
pkt->allocate();
}
}
}
void
MSHR::TargetList::replaceUpgrades()
{
if (!hasUpgrade)
return;
for (auto& t : *this) {
replaceUpgrade(t.pkt);
}
hasUpgrade = false;
}
void
MSHR::TargetList::clearDownstreamPending()
{
for (auto& t : *this) {
if (t.markedPending) {
// Iterate over the SenderState stack and see if we find
// an MSHR entry. If we find one, clear the
// downstreamPending flag by calling
// clearDownstreamPending(). This recursively clears the
// downstreamPending flag in all caches this packet has
// passed through.
MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
if (mshr != nullptr) {
mshr->clearDownstreamPending();
}
t.markedPending = false;
}
}
}
bool
MSHR::TargetList::checkFunctional(PacketPtr pkt)
{
for (auto& t : *this) {
if (pkt->checkFunctional(t.pkt)) {
return true;
}
}
return false;
}
void
MSHR::TargetList::print(std::ostream &os, int verbosity,
const std::string &prefix) const
{
for (auto& t : *this) {
const char *s;
switch (t.source) {
case Target::FromCPU:
s = "FromCPU";
break;
case Target::FromSnoop:
s = "FromSnoop";
break;
case Target::FromPrefetcher:
s = "FromPrefetcher";
break;
default:
s = "";
break;
}
ccprintf(os, "%s%s: ", prefix, s);
t.pkt->print(os, verbosity, "");
ccprintf(os, "\n");
}
}
void
MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
Tick when_ready, Counter _order, bool alloc_on_fill)
{
blkAddr = blk_addr;
blkSize = blk_size;
isSecure = target->isSecure();
readyTime = when_ready;
order = _order;
assert(target);
isForward = false;
_isUncacheable = target->req->isUncacheable();
inService = false;
downstreamPending = false;
assert(targets.isReset());
// Don't know of a case where we would allocate a new MSHR for a
// snoop (mem-side request), so set source according to request here
Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
Target::FromPrefetcher : Target::FromCPU;
targets.add(target, when_ready, _order, source, true, alloc_on_fill);
assert(deferredTargets.isReset());
}
void
MSHR::clearDownstreamPending()
{
assert(downstreamPending);
downstreamPending = false;
// recursively clear flag on any MSHRs we will be forwarding
// responses to
targets.clearDownstreamPending();
}
void
MSHR::markInService(bool pending_modified_resp)
{
assert(!inService);
inService = true;
pendingModified = targets.needsWritable || pending_modified_resp;
postInvalidate = postDowngrade = false;
if (!downstreamPending) {
// let upstream caches know that the request has made it to a
// level where it's going to get a response
targets.clearDownstreamPending();
}
}
void
MSHR::deallocate()
{
assert(targets.empty());
targets.resetFlags();
assert(deferredTargets.isReset());
inService = false;
}
/*
* Adds a target to an MSHR
*/
void
MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
bool alloc_on_fill)
{
// assume we'd never issue a prefetch when we've got an
// outstanding miss
assert(pkt->cmd != MemCmd::HardPFReq);
// uncacheable accesses always allocate a new MSHR, and cacheable
// accesses ignore any uncacheable MSHRs, thus we should never
// have targets addded if originally allocated uncacheable
assert(!_isUncacheable);
// if there's a request already in service for this MSHR, we will
// have to defer the new target until after the response if any of
// the following are true:
// - there are other targets already deferred
// - there's a pending invalidate to be applied after the response
// comes back (but before this target is processed)
// - the MSHR's first (and only) non-deferred target is a cache
// maintenance packet
// - the new target is a cache maintenance packet (this is probably
// overly conservative but certainly safe)
// - this target requires a writable block and either we're not
// getting a writable block back or we have already snooped
// another read request that will downgrade our writable block
// to non-writable (Shared or Owned)
PacketPtr tgt_pkt = targets.front().pkt;
if (pkt->req->isCacheMaintenance() ||
tgt_pkt->req->isCacheMaintenance() ||
!deferredTargets.empty() ||
(inService &&
(hasPostInvalidate() ||
(pkt->needsWritable() &&
(!isPendingModified() || hasPostDowngrade() || isForward))))) {
// need to put on deferred list
if (inService && hasPostInvalidate())
replaceUpgrade(pkt);
deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true,
alloc_on_fill);
} else {
// No request outstanding, or still OK to append to
// outstanding request: append to regular target list. Only
// mark pending if current request hasn't been issued yet
// (isn't in service).
targets.add(pkt, whenReady, _order, Target::FromCPU, !inService,
alloc_on_fill);
}
}
bool
MSHR::handleSnoop(PacketPtr pkt, Counter _order)
{
DPRINTF(Cache, "%s for %s\n", __func__, pkt->print());
// when we snoop packets the needsWritable and isInvalidate flags
// should always be the same, however, this assumes that we never
// snoop writes as they are currently not marked as invalidations
panic_if((pkt->needsWritable() != pkt->isInvalidate()) &&
!pkt->req->isCacheMaintenance(),
"%s got snoop %s where needsWritable, "
"does not match isInvalidate", name(), pkt->print());
if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
// Request has not been issued yet, or it's been issued
// locally but is buffered unissued at some downstream cache
// which is forwarding us this snoop. Either way, the packet
// we're snooping logically precedes this MSHR's request, so
// the snoop has no impact on the MSHR, but must be processed
// in the standard way by the cache. The only exception is
// that if we're an L2+ cache buffering an UpgradeReq from a
// higher-level cache, and the snoop is invalidating, then our
// buffered upgrades must be converted to read exclusives,
// since the upper-level cache no longer has a valid copy.
// That is, even though the upper-level cache got out on its
// local bus first, some other invalidating transaction
// reached the global bus before the upgrade did.
if (pkt->needsWritable() || pkt->req->isCacheInvalidate()) {
targets.replaceUpgrades();
deferredTargets.replaceUpgrades();
}
return false;
}
// From here on down, the request issued by this MSHR logically
// precedes the request we're snooping.
if (pkt->needsWritable() || pkt->req->isCacheInvalidate()) {
// snooped request still precedes the re-request we'll have to
// issue for deferred targets, if any...
deferredTargets.replaceUpgrades();
}
PacketPtr tgt_pkt = targets.front().pkt;
if (hasPostInvalidate() || tgt_pkt->req->isCacheInvalidate()) {
// a prior snoop has already appended an invalidation or a
// cache invalidation operation is in progress, so logically
// we don't have the block anymore; no need for further
// snooping.
return true;
}
if (isPendingModified() || pkt->isInvalidate()) {
// We need to save and replay the packet in two cases:
// 1. We're awaiting a writable copy (Modified or Exclusive),
// so this MSHR is the orgering point, and we need to respond
// after we receive data.
// 2. It's an invalidation (e.g., UpgradeReq), and we need
// to forward the snoop up the hierarchy after the current
// transaction completes.
// Start by determining if we will eventually respond or not,
// matching the conditions checked in Cache::handleSnoop
bool will_respond = isPendingModified() && pkt->needsResponse() &&
!pkt->isClean();
// The packet we are snooping may be deleted by the time we
// actually process the target, and we consequently need to
// save a copy here. Clear flags and also allocate new data as
// the original packet data storage may have been deleted by
// the time we get to process this packet. In the cases where
// we are not responding after handling the snoop we also need
// to create a copy of the request to be on the safe side. In
// the latter case the cache is responsible for deleting both
// the packet and the request as part of handling the deferred
// snoop.
PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
new Packet(new Request(*pkt->req), pkt->cmd, blkSize, pkt->id);
if (will_respond) {
// we are the ordering point, and will consequently
// respond, and depending on whether the packet
// needsWritable or not we either pass a Shared line or a
// Modified line
pkt->setCacheResponding();
// inform the cache hierarchy that this cache had the line
// in the Modified state, even if the response is passed
// as Shared (and thus non-writable)
pkt->setResponderHadWritable();
// in the case of an uncacheable request there is no need
// to set the responderHadWritable flag, but since the
// recipient does not care there is no harm in doing so
}
targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
downstreamPending && targets.needsWritable, false);
if (pkt->needsWritable() || pkt->isInvalidate()) {
// This transaction will take away our pending copy
postInvalidate = true;
}
if (isPendingModified() && pkt->isClean()) {
pkt->setSatisfied();
}
}
if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
// This transaction will get a read-shared copy, downgrading
// our copy if we had a writable one
postDowngrade = true;
// make sure that any downstream cache does not respond with a
// writable (and dirty) copy even if it has one, unless it was
// explicitly asked for one
pkt->setHasSharers();
}
return true;
}
MSHR::TargetList
MSHR::extractServiceableTargets(PacketPtr pkt)
{
TargetList ready_targets;
// If the downstream MSHR got an invalidation request then we only
// service the first of the FromCPU targets and any other
// non-FromCPU target. This way the remaining FromCPU targets
// issue a new request and get a fresh copy of the block and we
// avoid memory consistency violations.
if (pkt->cmd == MemCmd::ReadRespWithInvalidate) {
auto it = targets.begin();
assert((it->source == Target::FromCPU) ||
(it->source == Target::FromPrefetcher));
ready_targets.push_back(*it);
it = targets.erase(it);
while (it != targets.end()) {
if (it->source == Target::FromCPU) {
it++;
} else {
assert(it->source == Target::FromSnoop);
ready_targets.push_back(*it);
it = targets.erase(it);
}
}
ready_targets.populateFlags();
} else {
std::swap(ready_targets, targets);
}
targets.populateFlags();
return ready_targets;
}
bool
MSHR::promoteDeferredTargets()
{
if (targets.empty() && deferredTargets.empty()) {
// nothing to promote
return false;
}
// the deferred targets can be generally promoted unless they
// contain a cache maintenance request
// find the first target that is a cache maintenance request
auto it = std::find_if(deferredTargets.begin(), deferredTargets.end(),
[](MSHR::Target &t) {
return t.pkt->req->isCacheMaintenance();
});
if (it == deferredTargets.begin()) {
// if the first deferred target is a cache maintenance packet
// then we can promote provided the targets list is empty and
// we can service it on its own
if (targets.empty()) {
targets.splice(targets.end(), deferredTargets, it);
}
} else {
// if a cache maintenance operation exists, we promote all the
// deferred targets that precede it, or all deferred targets
// otherwise
targets.splice(targets.end(), deferredTargets,
deferredTargets.begin(), it);
}
deferredTargets.populateFlags();
targets.populateFlags();
order = targets.front().order;
readyTime = std::max(curTick(), targets.front().readyTime);
return true;
}
void
MSHR::promoteWritable()
{
if (deferredTargets.needsWritable &&
!(hasPostInvalidate() || hasPostDowngrade())) {
// We got a writable response, but we have deferred targets
// which are waiting to request a writable copy (not because
// of a pending invalidate). This can happen if the original
// request was for a read-only block, but we got a writable
// response anyway. Since we got the writable copy there's no
// need to defer the targets, so move them up to the regular
// target list.
assert(!targets.needsWritable);
targets.needsWritable = true;
// if any of the deferred targets were upper-level cache
// requests marked downstreamPending, need to clear that
assert(!downstreamPending); // not pending here anymore
deferredTargets.clearDownstreamPending();
// this clears out deferredTargets too
targets.splice(targets.end(), deferredTargets);
deferredTargets.resetFlags();
}
}
bool
MSHR::checkFunctional(PacketPtr pkt)
{
// For printing, we treat the MSHR as a whole as single entity.
// For other requests, we iterate over the individual targets
// since that's where the actual data lies.
if (pkt->isPrint()) {
pkt->checkFunctional(this, blkAddr, isSecure, blkSize, nullptr);
return false;
} else {
return (targets.checkFunctional(pkt) ||
deferredTargets.checkFunctional(pkt));
}
}
bool
MSHR::sendPacket(Cache &cache)
{
return cache.sendMSHRQueuePacket(this);
}
void
MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
{
ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
prefix, blkAddr, blkAddr + blkSize - 1,
isSecure ? "s" : "ns",
isForward ? "Forward" : "",
allocOnFill() ? "AllocOnFill" : "",
needsWritable() ? "Wrtbl" : "",
_isUncacheable ? "Unc" : "",
inService ? "InSvc" : "",
downstreamPending ? "DwnPend" : "",
postInvalidate ? "PostInv" : "",
postDowngrade ? "PostDowngr" : "");
if (!targets.empty()) {
ccprintf(os, "%s Targets:\n", prefix);
targets.print(os, verbosity, prefix + " ");
}
if (!deferredTargets.empty()) {
ccprintf(os, "%s Deferred Targets:\n", prefix);
deferredTargets.print(os, verbosity, prefix + " ");
}
}
std::string
MSHR::print() const
{
ostringstream str;
print(str);
return str.str();
}