7433d77fcf
This patch adds the necessary commands and cache functionality to allow clean writebacks. This functionality is crucial, especially when having exclusive (victim) caches. For example, if read-only L1 instruction caches are not sending clean writebacks, there will never be any spills from the L1 to the L2. At the moment the cache model defaults to not sending clean writebacks, and this should possibly be re-evaluated. The implementation of clean writebacks relies on a new packet command WritebackClean, which acts much like a Writeback (renamed WritebackDirty), and also much like a CleanEvict. On eviction of a clean block the cache either sends a clean evict, or a clean writeback, and if any copies are still cached upstream the clean evict/writeback is dropped. Similarly, if a clean evict/writeback reaches a cache where there are outstanding MSHRs for the block, the packet is dropped. In the typical case though, the clean writeback allocates a block in the downstream cache, and marks it writable if the evicted block was writable. The patch changes the O3_ARM_v7a L1 cache configuration and the default L1 caches in config/common/Caches.py
394 lines
15 KiB
C++
Executable file
394 lines
15 KiB
C++
Executable file
/*
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* Copyright (c) 2013-2015 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 "base/misc.hh"
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#include "base/trace.hh"
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#include "debug/SnoopFilter.hh"
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#include "mem/snoop_filter.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: packet src %s addr 0x%x cmd %s\n",
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__func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
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// Ultimately we should check if the packet came from an
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// allocating source, not just if the port is snooping
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bool allocate = !cpkt->req->isUncacheable() && slave_port.isSnooping();
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Addr line_addr = cpkt->getBlockAddr(linesize);
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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->memInhibitAsserted()) {
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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, const Packet* cpkt)
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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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assert(reqLookupResult->first == cpkt->getBlockAddr(linesize));
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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 addr 0x%x cmd %s\n",
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__func__, cpkt->getAddr(), cpkt->cmdString());
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assert(cpkt->isRequest());
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Addr line_addr = cpkt->getBlockAddr(linesize);
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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->needsExclusive()));
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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: packet rsp %s req %s addr 0x%x cmd %s\n",
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__func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
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cpkt->cmdString());
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assert(cpkt->isResponse());
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assert(cpkt->memInhibitAsserted());
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// Ultimately we should check if the packet came from an
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// allocating source, not just if the port is snooping
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bool allocate = !cpkt->req->isUncacheable() && req_port.isSnooping();
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if (!allocate)
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return;
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Addr line_addr = cpkt->getBlockAddr(linesize);
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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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// Update the residency of the cache line.
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if (cpkt->needsExclusive() || !cpkt->sharedAsserted()) {
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DPRINTF(SnoopFilter, "%s: dropping %x because needs: %i shared: %i "\
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"SF val: %x.%x\n", __func__, rsp_mask,
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cpkt->needsExclusive(), cpkt->sharedAsserted(),
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sf_item.requested, sf_item.holder);
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sf_item.holder &= ~rsp_mask;
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// The snoop filter does not see any ACKs from non-responding sharers
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// that have been invalidated :( So below assert would be nice, but..
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//assert(sf_item.holder == 0);
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sf_item.holder = 0;
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}
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assert(!cpkt->isWriteback());
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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: packet rsp %s req %s addr 0x%x cmd %s\n",
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__func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
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cpkt->cmdString());
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assert(cpkt->isResponse());
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assert(cpkt->memInhibitAsserted());
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Addr line_addr = cpkt->getBlockAddr(linesize);
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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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// Remote (to this snoop filter) snoops update the filter
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// already when they arrive from below, because we may not see
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// any response.
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if (cpkt->needsExclusive()) {
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// If the request to this snoop response hit an in-flight
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// transaction,
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// the holder was not reset -> no assertion & do that here, now!
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//assert(sf_item.holder == 0);
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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: packet src %s addr 0x%x cmd %s\n",
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__func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
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assert(cpkt->isResponse());
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// Ultimately we should check if the packet came from an
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// allocating source, not just if the port is snooping
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bool allocate = !cpkt->req->isUncacheable() && slave_port.isSnooping();
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if (!allocate)
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return;
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Addr line_addr = cpkt->getBlockAddr(linesize);
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SnoopMask slave_mask = portToMask(slave_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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// 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. Here we assume that the
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// line has been zapped in all caches that are not the responder.
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if (cpkt->needsExclusive() || !cpkt->sharedAsserted())
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sf_item.holder = 0;
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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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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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