Re: [Gems-users] instruction count

["Zhang Yu" <thuzhangyu@xxxxxxxxx>]

Thanks. I just want to run some application on different configurations. Since it will take very long time for the whole application to complete, I can only afford to run it partially. So, what I do is making the simulation run for a certain number of cycles. Then, the number of instructions executed would be a metric of performance. That's why I care so much about this. If the instruction counts is not reliable, what would you suggest me to do?

Thanks,
Yu

On Jan 29, 2008 2:00 PM, Dan Gibson <degibson@xxxxxxxx> wrote:

I think the user/OS instruction counts are subject to a lot of factors.
The 'init' process on Linux for instance is user-level. I'm not sure if
there is an analogue on Solaris or not, but relying on instruction
counts is not a good idea anyway for multiprocessor systems, since
multiprocessors will often experience entirely different execution paths
from run to run.

Zhang Yu wrote:
> I only care the number of instructions from the user. pstats gives two
> kind of instruction count, one is from the user and the other is from
> the supervisor, I guess the OS idle loop may increase the instruction
> counts of the supervisor but will not impact that of the user.
>
> Thanks,
> Yu
>
> On Jan 29, 2008 1:47 PM, Dan Gibson <degibson@xxxxxxxx

> <mailto:degibson@xxxxxxxx>> wrote:
>
>     Processors will always execute SOME code somewhere -- pstats is
>     agnostic
>     to which code is executed. That is, even the execution of the OS idle
>     loop will cause the pstats instruction counts to increment-- you
>     cannot
>     assume processors that you do not assign tasks do not execute
>     instructions.
>
>     Zhang Yu wrote:
>     > Thanks for the reply. However, what I mean of pstats is already a
>     > delta of the instructions (I did the calculation myself). And in my
>     > case, the number of instructions executed by each processor
>     should not
>     > be equal or similar.
>     >
>     > Yu
>     >
>     > On Jan 29, 2008 12:15 PM, Dan Gibson <degibson@xxxxxxxx
>     <mailto:degibson@xxxxxxxx>

>     > <mailto:degibson@xxxxxxxx <mailto:degibson@xxxxxxxx>>> wrote:
>     >
>     >     The number of instructions reported by ruby is a delta
>     between the
>     >     initial instruction count and the final instruction count. The
>     >     number of
>     >     instructions reported by pstats is a total instruction count,
>     >     staring at
>     >     boot-time if I am not mistaken. Hence the discrepancy.
>     >
>     >     Zhang Yu wrote:
>     >     > Hi,
>     >     >
>     >     > I'm using Gems2.0 with Simics3.0.30. While I run the
>     simulation with
>     >     > multiple cores, the statistics dumped by ruby seems to be
>     >     > unreasonable. For example, when I use "taskset" command to
>     assign a
>     >     > single task to a certain processor, instruction_executed
>     for all the
>     >     > processors are almost the same in the ruby statistics.
>     However, if I
>     >     > use "pstats" command in simics, I can see obviously that
>     the certain
>     >     > processor executed much more instructions than other
>     processors. So,
>     >     > is there anything I can do to make the ruby stats seems more
>     >     reasonable?
>     >     >
>     >     > Thanks,
>     >     > Yu
>     >     >
>     >
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