Hi Xiangyang,
Thanks for your information.
"if this inst is squashed, meaning we need to get this inst out of
pipeline. And the method to get this inst out of pipeline is to set the
flags"
This is something I'm a little confused. If we decide to squash an
instruction, why this instruction still need to go through pipelines,
instead of directly removing it and younger instructions from the same
thread in ROB and some related queues, and free resources.
Another related question is during branch mis-prediction, what steps the
simulator will go through to correct the execution? Which code I should
take a look about this?
In various CPU design, branch speculative execution can be handled in
different pipe stages, so I'm wondering how gem5 handle this in simulation.
Thanks again for your advice.
On 7/29/2013 5:50 PM, Xiangyang Guo wrote:
Hi, Jianghao,
I guess the main purpose of setCanCommit or setExecuted is to forward
this instruction to the next stage. Because if one inst is in the
pipeline, we set different flags to this inst( to indicate which stage
this inst is), if this inst is squashed, meaning we need to get this
inst out of pipeline. And the method to get this inst out of pipeline
is to set the flags (CanCommit() or Executed()), otherwise we will get
deadlock. Of course, I may be wrong. Hope other guys can give you more
detailed explain.
Regards
Xiangyang
On Mon, Jul 29, 2013 at 2:38 PM, Jianghao Guo <[email protected]
<mailto:[email protected]>> wrote:
How is squash handled in gem5 o3 CPU? What's exactly done in squash?
From codes under src/cpu/o3, there are squash functions defined in
different pipeline resources, like iew, inst_queue, lsq etc. Does
this mean each part can initialize squash?
In following code, when an instruction is squashed, why we still
set it as Executed and canCommited?
Thanks
DefaultIEW<Impl>::executeInsts()
// Check if the instruction is squashed; if so then skip it
if (inst->isSquashed()) {
inst->setExecuted();
inst->setCanCommit();
++iewExecSquashedInsts;
decrWb(inst->seqNum);
continue;
}
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