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authorNilay Vaish <nilay@cs.wisc.edu>2011-02-12 11:41:20 -0600
committerNilay Vaish <nilay@cs.wisc.edu>2011-02-12 11:41:20 -0600
commit0cede15d6c5213d83e4cd143014321b2ee7ec5eb (patch)
tree2bff094d29f493d61a63cba2fb9a04f409d9e120 /src/mem/protocol/MOESI_CMP_token-L1cache.sm
parent2971b8401a4a76a774962900d9aed6e9eb4b2950 (diff)
downloadgem5-0cede15d6c5213d83e4cd143014321b2ee7ec5eb.tar.xz
Ruby: Reorder Cache Lookup in Protocol Files
The patch changes the order in which L1 dcache and icache are looked up when a request comes in. Earlier, if a request came in for instruction fetch, the dcache was looked up before the icache, to correctly handle self-modifying code. But, in the common case, dcache is going to report a miss and the subsequent icache lookup is going to report a hit. Given the invariant - caches under the same controller keep track of disjoint sets of cache blocks, we can move the icache lookup before the dcache lookup. In case of a hit in the icache, using our invariant, we know that the dcache would have reported a miss. In case of a miss in the icache, we know that icache would have missed even if the dcache was looked up before looking up the icache. Effectively, we are doing the same thing as before, though in the common case, we expect reduction in the number of lookups. This was empirically confirmed for MOESI hammer. The ratio lookups to access requests is now about 1.1 to 1.
Diffstat (limited to 'src/mem/protocol/MOESI_CMP_token-L1cache.sm')
-rw-r--r--src/mem/protocol/MOESI_CMP_token-L1cache.sm35
1 files changed, 18 insertions, 17 deletions
diff --git a/src/mem/protocol/MOESI_CMP_token-L1cache.sm b/src/mem/protocol/MOESI_CMP_token-L1cache.sm
index 00e9404c9..226f21374 100644
--- a/src/mem/protocol/MOESI_CMP_token-L1cache.sm
+++ b/src/mem/protocol/MOESI_CMP_token-L1cache.sm
@@ -647,20 +647,21 @@ machine(L1Cache, "Token protocol")
if (in_msg.Type == CacheRequestType:IFETCH) {
// ** INSTRUCTION ACCESS ***
- // Check to see if it is in the OTHER L1
- Entry L1Dcache_entry := getL1DCacheEntry(in_msg.LineAddress);
- if (is_valid(L1Dcache_entry)) {
- // The block is in the wrong L1, try to write it to the L2
- trigger(Event:L1_Replacement, in_msg.LineAddress,
- L1Dcache_entry, tbe);
- }
-
Entry L1Icache_entry := getL1ICacheEntry(in_msg.LineAddress);
if (is_valid(L1Icache_entry)) {
// The tag matches for the L1, so the L1 fetches the line. We know it can't be in the L2 due to exclusion
trigger(mandatory_request_type_to_event(in_msg.Type),
in_msg.LineAddress, L1Icache_entry, tbe);
} else {
+
+ // Check to see if it is in the OTHER L1
+ Entry L1Dcache_entry := getL1DCacheEntry(in_msg.LineAddress);
+ if (is_valid(L1Dcache_entry)) {
+ // The block is in the wrong L1, try to write it to the L2
+ trigger(Event:L1_Replacement, in_msg.LineAddress,
+ L1Dcache_entry, tbe);
+ }
+
if (L1IcacheMemory.cacheAvail(in_msg.LineAddress)) {
// L1 does't have the line, but we have space for it in the L1
trigger(mandatory_request_type_to_event(in_msg.Type),
@@ -676,21 +677,21 @@ machine(L1Cache, "Token protocol")
} else {
// *** DATA ACCESS ***
- // Check to see if it is in the OTHER L1
- Entry L1Icache_entry := getL1ICacheEntry(in_msg.LineAddress);
-
- if (is_valid(L1Icache_entry)) {
- // The block is in the wrong L1, try to write it to the L2
- trigger(Event:L1_Replacement, in_msg.LineAddress,
- L1Icache_entry, tbe);
- }
-
Entry L1Dcache_entry := getL1DCacheEntry(in_msg.LineAddress);
if (is_valid(L1Dcache_entry)) {
// The tag matches for the L1, so the L1 fetches the line. We know it can't be in the L2 due to exclusion
trigger(mandatory_request_type_to_event(in_msg.Type),
in_msg.LineAddress, L1Dcache_entry, tbe);
} else {
+
+ // Check to see if it is in the OTHER L1
+ Entry L1Icache_entry := getL1ICacheEntry(in_msg.LineAddress);
+ if (is_valid(L1Icache_entry)) {
+ // The block is in the wrong L1, try to write it to the L2
+ trigger(Event:L1_Replacement, in_msg.LineAddress,
+ L1Icache_entry, tbe);
+ }
+
if (L1DcacheMemory.cacheAvail(in_msg.LineAddress)) {
// L1 does't have the line, but we have space for it in the L1
trigger(mandatory_request_type_to_event(in_msg.Type),