Re: [gem5-users] About the rename and dispatch stages in O3CPU

[GE ZHIGUO]

Hi, Xangyang

     I think you are right. And I now have a better understanding to the 
pipeline implementation.
Thanks a lot!

Zhiguo

From: gem5-users-boun...@gem5.org [mailto:gem5-users-boun...@gem5.org] On 
Behalf Of Xiangyang Guo
Sent: Wednesday, August 14, 2013 8:13 PM
To: gem5 users mailing list
Subject: Re: [gem5-users] About the rename and dispatch stages in O3CPU

By the way, I guess the the code of "insert inst to ROB" is located in the 
commit_impl.hh  doesn't mean this one inst is inserted into ROB at commit 
stage. I think It means every cycle, there are insts inserted into ROB from 
rename stage. I mean when pipeline works, every cycle, we check if there are 
insts available to insert into ROB, if yes, then insert it. So I guess Gem5 
inserts the inst into ROB after renaming finish.

Someone who is familiar with this could correct me.

On Wed, Aug 14, 2013 at 1:45 AM, GE ZHIGUO 
<ge.zhi...@huawei.com<mailto:ge.zhi...@huawei.com>> wrote:
Hi, Henry

Thanks for your reply!
Yes, so this is even more confusing to me.
In real CPU, when(in which stage) the instructions are put into ROB?

Regards

Zhiguo








From: gem5-users-boun...@gem5.org<mailto:gem5-users-boun...@gem5.org> 
[mailto:gem5-users-boun...@gem5.org<mailto:gem5-users-boun...@gem5.org>] On 
Behalf Of Huang, Henry
Sent: Wednesday, August 14, 2013 12:19 PM

To: gem5 users mailing list
Subject: Re: [gem5-users] About the rename and dispatch stages in O3CPU


I think code in commit_impl.hh inserts renamed insts into ROB.



#0  ROB<O3CPUImpl>::insertInst (this=0x27d8100, inst=...) at 
build/ALPHA/cpu/o3/rob_impl.hh:206

#1  0x0000000000b44936 in DefaultCommit<O3CPUImpl>::getInsts (this=0x27d79a8) 
at build/ALPHA/cpu/o3/commit_impl.hh:1318

#2  0x0000000000b34084 in DefaultCommit<O3CPUImpl>::commit (this=0x27d79a8) at 
build/ALPHA/cpu/o3/commit_impl.hh:884

#3  0x0000000000b30d0e in DefaultCommit<O3CPUImpl>::tick (this=0x27d79a8) at 
build/ALPHA/cpu/o3/commit_impl.hh:669

#4  0x0000000000b533fd in FullO3CPU<O3CPUImpl>::tick (this=0x27d4ff0) at 
build/ALPHA/cpu/o3/cpu.cc:604

#5  0x0000000000b6538e in FullO3CPU<O3CPUImpl>::TickEvent::process 
(this=0x27d50f8) at build/ALPHA/cpu/o3/cpu.cc:138

#6  0x0000000000762542 in EventQueue::serviceOne (this=0x193d2b0) at 
build/ALPHA/sim/eventq.cc:204



1296 void

1297 DefaultCommit<Impl>::getInsts()

1298 {

1299     DPRINTF(Commit, "Getting instructions from Rename stage.\n");

1300

1301     // Read any renamed instructions and place them into the ROB.

1302     int insts_to_process = std::min((int)renameWidth, fromRename->size);

1303

1304     for (int inst_num = 0; inst_num < insts_to_process; ++inst_num) {

1305         DynInstPtr inst;

1306

1307         inst = fromRename->insts[inst_num];





Thanks,


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-----Original Message-----
From: gem5-users-boun...@gem5.org<mailto:gem5-users-boun...@gem5.org> 
[mailto:gem5-users-boun...@gem5.org<mailto:gem5-users-boun...@gem5.org>] On 
Behalf Of GE ZHIGUO
Sent: Wednesday, August 14, 2013 11:59 AM
To: gem5 users mailing list
Subject: [gem5-users] About the rename and dispatch stages in O3CPU



Hi,



I have a question about O3CPU pipeline in GEM5.

My understanding about the GEM5 O3CPU is that rename stage does not put 
instructions into instruction queue(issue queue) and ROB. Dispatch stage 
actually does the above. So, rename + dispatch in GEM5 is actually the rename 
stage of O3CPU. Please correct me if I am wrong.

As the dispatch stage pushes the instructions into ROB and instruction Queue, I 
think that the free entries of ROB and instruction queue should be checked at 
this stage. However, the rename stage in gem5 check the free ROB and 
instruction queue size.

I cannot understand this. Can anyone help explain?



Thanks!



Zhiguo







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