[PTLsim-devel] Cause of inaccurate simulated cycle number?

[Lixia Liu]

Yes, I do expect to see different number from different micro-architectures.

But this kind of large difference should have a reason. 

Especially I'd like to see how to extend the ptl's OOO core to simulate
Intel microarchitecture. There, any suggestion on that is appreciated.

Thanks.

-----Original Message-----
From: xi yang [mailto:hiyangxi at gmail.com] 
Sent: Thursday, August 19, 2010 6:27 PM
To: Lixia Liu
Cc: ptlsim-devel at ptlsim.org
Subject: Re: [PTLsim-devel] Cause of inaccurate simulated cycle number?

On Fri, Aug 20, 2010 at 8:02 AM, Lixia Liu <lixia789 at gmail.com> wrote:
> Hello.
>
> I am using ptlsim (userspace) to simulate sequential code on Intel
multicore
> (Q6600). I found that
>
> sometimes it gives more than twice cycles # than hardware performance
> counter.
So, you compared two micro-architecture: Intel Core2 VS PTLsim OOO core.
If you run the same program in AMD K10 and Intel Core2, you will get
different numbers.
If you run the same program in Intel nehalem and Intel Core2, you will
get different numbers.


Regards.
>
> One example is something like below.
>
>    int tmp = 1;
>
>    for (int i=0; i<100000; i++)
>
>    {
>
>       tmp = tmp + tmp*2;
>
>    }
>
> The code is compiled by G++ 4.3.4 with –O3 option. The generated assembly
> code is quite simple.
>
> 4008a0:   83 c0 01                add    $0x1,%eax
>
> 4008a3:   8d 1c 5b                lea    (%rbx,%rbx,2),%ebx
>
> 4008a6:   3d a0 86 01 00       cmp    $0x186a0,%eax
>
> 4008ab:   75 f3                     jne    4008a0
>
> Measured results:
>
>         Ptlsim: 400042 instructions and 407505 cycles
>
>         Performance counter by Pfmon: 402333 instructions and 171829
cycles
>
> Does anyone have idea on the problem and how to fix it? Thanks!
>
> Best Regards,
>
> Lixia
>
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