5ebb8ec46b
When the snoopFilter receives a response, it updates its state using the hasSharers flag (indicates whether there are more than one copies of the block in the caches above). The hasSharers flag of the packet was previously populated when the request was traversing and snooping the caches looking for the block. 1) When the response is coming from the memory-side port, its order with respect to other responses is not necessarily preserved (e.g., a request that arrived second to the xbar can get its response first). As a result the snoopFilter might process responses out of order updating its residency information using the non valid hasSharers flag which was populated much earlier. 2) When the response is from an on-chip, the MSHRs preserve a well defined order and the hasSharers flag should contain valid information. This patch changes the snoopFilter by avoiding the hasSharers flag when the response is from the memory-side port. Change-Id: Ib2d22a5b7bf3eccac64445127d2ea20ee74bb25b Reviewed-by: Andreas Hansson <andreas.hansson@arm.com> Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
409 lines
15 KiB
C++
Executable file
409 lines
15 KiB
C++
Executable file
/*
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* Copyright (c) 2013-2016 ARM Limited
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* All rights reserved
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*
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* The license below extends only to copyright in the software and shall
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* not be construed as granting a license to any other intellectual
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* property including but not limited to intellectual property relating
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* to a hardware implementation of the functionality of the software
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* licensed hereunder. You may use the software subject to the license
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* terms below provided that you ensure that this notice is replicated
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* unmodified and in its entirety in all distributions of the software,
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* modified or unmodified, in source code or in binary form.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Stephan Diestelhorst
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*/
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/**
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* @file
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* Implementation of a snoop filter.
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*/
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#include "mem/snoop_filter.hh"
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#include "base/misc.hh"
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#include "base/trace.hh"
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#include "debug/SnoopFilter.hh"
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#include "sim/system.hh"
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void
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SnoopFilter::eraseIfNullEntry(SnoopFilterCache::iterator& sf_it)
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{
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SnoopItem& sf_item = sf_it->second;
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if (!(sf_item.requested | sf_item.holder)) {
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cachedLocations.erase(sf_it);
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DPRINTF(SnoopFilter, "%s: Removed SF entry.\n",
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__func__);
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}
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}
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std::pair<SnoopFilter::SnoopList, Cycles>
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SnoopFilter::lookupRequest(const Packet* cpkt, const SlavePort& slave_port)
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{
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DPRINTF(SnoopFilter, "%s: src %s packet %s\n", __func__,
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slave_port.name(), cpkt->print());
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// check if the packet came from a cache
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bool allocate = !cpkt->req->isUncacheable() && slave_port.isSnooping() &&
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cpkt->fromCache();
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Addr line_addr = cpkt->getBlockAddr(linesize);
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if (cpkt->isSecure()) {
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line_addr |= LineSecure;
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}
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SnoopMask req_port = portToMask(slave_port);
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reqLookupResult = cachedLocations.find(line_addr);
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bool is_hit = (reqLookupResult != cachedLocations.end());
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// If the snoop filter has no entry, and we should not allocate,
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// do not create a new snoop filter entry, simply return a NULL
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// portlist.
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if (!is_hit && !allocate)
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return snoopDown(lookupLatency);
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// If no hit in snoop filter create a new element and update iterator
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if (!is_hit)
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reqLookupResult = cachedLocations.emplace(line_addr, SnoopItem()).first;
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SnoopItem& sf_item = reqLookupResult->second;
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SnoopMask interested = sf_item.holder | sf_item.requested;
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// Store unmodified value of snoop filter item in temp storage in
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// case we need to revert because of a send retry in
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// updateRequest.
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retryItem = sf_item;
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totRequests++;
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if (is_hit) {
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// Single bit set -> value is a power of two
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if (isPow2(interested))
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hitSingleRequests++;
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else
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hitMultiRequests++;
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}
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DPRINTF(SnoopFilter, "%s: SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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// If we are not allocating, we are done
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if (!allocate)
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return snoopSelected(maskToPortList(interested & ~req_port),
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lookupLatency);
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if (cpkt->needsResponse()) {
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if (!cpkt->cacheResponding()) {
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// Max one request per address per port
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panic_if(sf_item.requested & req_port, "double request :( " \
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"SF value %x.%x\n", sf_item.requested, sf_item.holder);
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// Mark in-flight requests to distinguish later on
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sf_item.requested |= req_port;
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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} else {
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// NOTE: The memInhibit might have been asserted by a cache closer
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// to the CPU, already -> the response will not be seen by this
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// filter -> we do not need to keep the in-flight request, but make
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// sure that we know that that cluster has a copy
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panic_if(!(sf_item.holder & req_port), "Need to hold the value!");
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DPRINTF(SnoopFilter,
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"%s: not marking request. SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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}
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} else { // if (!cpkt->needsResponse())
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assert(cpkt->isEviction());
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// make sure that the sender actually had the line
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panic_if(!(sf_item.holder & req_port), "requester %x is not a " \
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"holder :( SF value %x.%x\n", req_port,
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sf_item.requested, sf_item.holder);
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// CleanEvicts and Writebacks -> the sender and all caches above
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// it may not have the line anymore.
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if (!cpkt->isBlockCached()) {
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sf_item.holder &= ~req_port;
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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}
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}
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return snoopSelected(maskToPortList(interested & ~req_port), lookupLatency);
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}
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void
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SnoopFilter::finishRequest(bool will_retry, Addr addr, bool is_secure)
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{
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if (reqLookupResult != cachedLocations.end()) {
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// since we rely on the caller, do a basic check to ensure
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// that finishRequest is being called following lookupRequest
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Addr line_addr = (addr & ~(Addr(linesize - 1)));
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if (is_secure) {
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line_addr |= LineSecure;
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}
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assert(reqLookupResult->first == line_addr);
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if (will_retry) {
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// Undo any changes made in lookupRequest to the snoop filter
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// entry if the request will come again. retryItem holds
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// the previous value of the snoopfilter entry.
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reqLookupResult->second = retryItem;
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DPRINTF(SnoopFilter, "%s: restored SF value %x.%x\n",
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__func__, retryItem.requested, retryItem.holder);
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}
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eraseIfNullEntry(reqLookupResult);
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}
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}
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std::pair<SnoopFilter::SnoopList, Cycles>
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SnoopFilter::lookupSnoop(const Packet* cpkt)
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{
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DPRINTF(SnoopFilter, "%s: packet %s\n", __func__, cpkt->print());
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assert(cpkt->isRequest());
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Addr line_addr = cpkt->getBlockAddr(linesize);
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if (cpkt->isSecure()) {
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line_addr |= LineSecure;
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}
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auto sf_it = cachedLocations.find(line_addr);
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bool is_hit = (sf_it != cachedLocations.end());
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panic_if(!is_hit && (cachedLocations.size() >= maxEntryCount),
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"snoop filter exceeded capacity of %d cache blocks\n",
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maxEntryCount);
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// If the snoop filter has no entry, simply return a NULL
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// portlist, there is no point creating an entry only to remove it
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// later
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if (!is_hit)
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return snoopDown(lookupLatency);
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SnoopItem& sf_item = sf_it->second;
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DPRINTF(SnoopFilter, "%s: old SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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SnoopMask interested = (sf_item.holder | sf_item.requested);
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totSnoops++;
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// Single bit set -> value is a power of two
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if (isPow2(interested))
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hitSingleSnoops++;
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else
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hitMultiSnoops++;
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// ReadEx and Writes require both invalidation and exlusivity, while reads
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// require neither. Writebacks on the other hand require exclusivity but
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// not the invalidation. Previously Writebacks did not generate upward
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// snoops so this was never an aissue. Now that Writebacks generate snoops
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// we need to special case for Writebacks.
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assert(cpkt->isWriteback() || cpkt->req->isUncacheable() ||
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(cpkt->isInvalidate() == cpkt->needsWritable()));
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if (cpkt->isInvalidate() && !sf_item.requested) {
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// Early clear of the holder, if no other request is currently going on
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// @todo: This should possibly be updated even though we do not filter
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// upward snoops
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sf_item.holder = 0;
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}
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eraseIfNullEntry(sf_it);
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x interest: %x \n",
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__func__, sf_item.requested, sf_item.holder, interested);
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return snoopSelected(maskToPortList(interested), lookupLatency);
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}
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void
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SnoopFilter::updateSnoopResponse(const Packet* cpkt,
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const SlavePort& rsp_port,
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const SlavePort& req_port)
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{
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DPRINTF(SnoopFilter, "%s: rsp %s req %s packet %s\n",
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__func__, rsp_port.name(), req_port.name(), cpkt->print());
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assert(cpkt->isResponse());
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assert(cpkt->cacheResponding());
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// if this snoop response is due to an uncacheable request, or is
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// being turned into a normal response, there is nothing more to
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// do
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if (cpkt->req->isUncacheable() || !req_port.isSnooping()) {
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return;
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}
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Addr line_addr = cpkt->getBlockAddr(linesize);
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if (cpkt->isSecure()) {
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line_addr |= LineSecure;
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}
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SnoopMask rsp_mask = portToMask(rsp_port);
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SnoopMask req_mask = portToMask(req_port);
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SnoopItem& sf_item = cachedLocations[line_addr];
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DPRINTF(SnoopFilter, "%s: old SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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// The source should have the line
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panic_if(!(sf_item.holder & rsp_mask), "SF value %x.%x does not have "\
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"the line\n", sf_item.requested, sf_item.holder);
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// The destination should have had a request in
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panic_if(!(sf_item.requested & req_mask), "SF value %x.%x missing "\
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"the original request\n", sf_item.requested, sf_item.holder);
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// If the snoop response has no sharers the line is passed in
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// Modified state, and we know that there are no other copies, or
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// they will all be invalidated imminently
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if (!cpkt->hasSharers()) {
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DPRINTF(SnoopFilter,
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"%s: dropping %x because non-shared snoop "
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"response SF val: %x.%x\n", __func__, rsp_mask,
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sf_item.requested, sf_item.holder);
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sf_item.holder = 0;
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}
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assert(!cpkt->isWriteback());
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// @todo Deal with invalidating responses
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sf_item.holder |= req_mask;
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sf_item.requested &= ~req_mask;
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assert(sf_item.requested | sf_item.holder);
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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}
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void
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SnoopFilter::updateSnoopForward(const Packet* cpkt,
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const SlavePort& rsp_port, const MasterPort& req_port)
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{
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DPRINTF(SnoopFilter, "%s: rsp %s req %s packet %s\n",
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__func__, rsp_port.name(), req_port.name(), cpkt->print());
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assert(cpkt->isResponse());
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assert(cpkt->cacheResponding());
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Addr line_addr = cpkt->getBlockAddr(linesize);
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if (cpkt->isSecure()) {
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line_addr |= LineSecure;
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}
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auto sf_it = cachedLocations.find(line_addr);
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bool is_hit = sf_it != cachedLocations.end();
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// Nothing to do if it is not a hit
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if (!is_hit)
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return;
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SnoopItem& sf_item = sf_it->second;
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DPRINTF(SnoopFilter, "%s: old SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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// If the snoop response has no sharers the line is passed in
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// Modified state, and we know that there are no other copies, or
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// they will all be invalidated imminently
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if (!cpkt->hasSharers()) {
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sf_item.holder = 0;
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}
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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eraseIfNullEntry(sf_it);
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}
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void
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SnoopFilter::updateResponse(const Packet* cpkt, const SlavePort& slave_port)
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{
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DPRINTF(SnoopFilter, "%s: src %s packet %s\n",
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__func__, slave_port.name(), cpkt->print());
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assert(cpkt->isResponse());
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// we only allocate if the packet actually came from a cache, but
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// start by checking if the port is snooping
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if (cpkt->req->isUncacheable() || !slave_port.isSnooping())
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return;
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// next check if we actually allocated an entry
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Addr line_addr = cpkt->getBlockAddr(linesize);
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if (cpkt->isSecure()) {
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line_addr |= LineSecure;
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}
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auto sf_it = cachedLocations.find(line_addr);
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if (sf_it == cachedLocations.end())
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return;
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SnoopMask slave_mask = portToMask(slave_port);
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SnoopItem& sf_item = sf_it->second;
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DPRINTF(SnoopFilter, "%s: old SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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// Make sure we have seen the actual request, too
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panic_if(!(sf_item.requested & slave_mask), "SF value %x.%x missing "\
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"request bit\n", sf_item.requested, sf_item.holder);
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// Update the residency of the cache line.
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sf_item.holder |= slave_mask;
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sf_item.requested &= ~slave_mask;
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assert(sf_item.holder | sf_item.requested);
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DPRINTF(SnoopFilter, "%s: new SF value %x.%x\n",
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__func__, sf_item.requested, sf_item.holder);
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}
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void
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SnoopFilter::regStats()
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{
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SimObject::regStats();
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totRequests
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.name(name() + ".tot_requests")
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.desc("Total number of requests made to the snoop filter.");
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hitSingleRequests
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.name(name() + ".hit_single_requests")
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.desc("Number of requests hitting in the snoop filter with a single "\
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"holder of the requested data.");
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hitMultiRequests
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.name(name() + ".hit_multi_requests")
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.desc("Number of requests hitting in the snoop filter with multiple "\
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"(>1) holders of the requested data.");
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totSnoops
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.name(name() + ".tot_snoops")
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.desc("Total number of snoops made to the snoop filter.");
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hitSingleSnoops
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.name(name() + ".hit_single_snoops")
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.desc("Number of snoops hitting in the snoop filter with a single "\
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"holder of the requested data.");
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hitMultiSnoops
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.name(name() + ".hit_multi_snoops")
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.desc("Number of snoops hitting in the snoop filter with multiple "\
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"(>1) holders of the requested data.");
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}
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SnoopFilter *
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SnoopFilterParams::create()
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{
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return new SnoopFilter(this);
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}
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