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cpu: o3: lsq: Fix TSO implementation

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This patch fixes violation of TSO in the O3CPU, as all loads must be
ordered with all other loads. In the LQ, if a snoop is observed, all
subsequent loads need to be squashed if the system is TSO.

Prior to this patch, the following case could be violated:

 P0         | P1          ;
 MOV [x],mail=/usr/spool/mail/nilay | MOV EAX,[y] ;
 MOV [y],mail=/usr/spool/mail/nilay | MOV EBX,[x] ;

exists (1:EAX=1 /\ 1:EBX=0) [is a violation]

The problem was found using litmus [http://diy.inria.fr].

Committed by: Nilay Vaish <nilay@cs.wisc.edu
This commit is contained in:
Marco Elver 2014-03-25 13:15:04 -05:00
parent 8b4b1dcb86
commit b884fcf412
1 changed files with 10 additions and 2 deletions
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12
src/cpu/o3/lsq_unit_impl.hh
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@ -464,6 +464,8 @@ LSQUnit<Impl>::checkSnoop(PacketPtr pkt)
incrLdIdx(load_idx);
bool force_squash = false;
while (load_idx != loadTail) {
DynInstPtr ld_inst = loadQueue[load_idx];
@ -476,8 +478,14 @@ LSQUnit<Impl>::checkSnoop(PacketPtr pkt)
DPRINTF(LSQUnit, "-- inst [sn:%lli] load_addr: %#x to pktAddr:%#x\n",
ld_inst->seqNum, load_addr, invalidate_addr);
if (load_addr == invalidate_addr) {
if (ld_inst->possibleLoadViolation()) {
if (load_addr == invalidate_addr || force_squash) {
if (needsTSO) {
// If we have a TSO system, as all loads must be ordered with
// all other loads, this load as well as *all* subsequent loads
// need to be squashed to prevent possible load reordering.
force_squash = true;
}
if (ld_inst->possibleLoadViolation() || force_squash) {
DPRINTF(LSQUnit, "Conflicting load at addr %#x [sn:%lli]\n",
pkt->getAddr(), ld_inst->seqNum);