[LLVMdev] A simulation tool

[Giridhar S]

I have never used CodeAnalyst first-hand, but the slow-down figures
that you quote lead me to believe that it must use hardware
performance counters. Instrumentation based profilers rarely, if ever,
display such low overhead. Also, instrumentation based profilers
cannot profile kernel routines, unless there is explicit support from
within the kernel (such as in Sun Solaris 10 and DTrace).

Taking a quick look at AMD's website seems to confirm this theory:
http://developer.amd.com/Assets/Basic_Performance_Measurements.pdf

If this topic is getting out-of-scope for the LLVM Dev list, we can
take it offline.

On Tue, Sep 1, 2009 at 10:32 PM, OvermindDL1<overminddl1 at gmail.com> wrote:
> Helps if I send it to the list....
>
> On Tue, Sep 1, 2009 at 5:33 PM, Giridhar S<thisisgiri at gmail.com> wrote:
>> Oprofile for Linux is a pretty good alternative.
>> (http://oprofile.sourceforge.net/about/)
>>
>> It uses hardware performance counters to collect profiling information
>> and therefore has very low overhead, whereas Valgrind performs dynamic
>> binary instrumentation and can be significantly slow (20-50x slower).
>> In addition, Cachegrind 'simulates' cache behavior through it's own
>> cache model, whereas Oprofile (or other counter based profilers)
>> report real cache events.
>>
>> Depending on what your needs are (ease of use, runtime overhead, etc)
>> you could pick either.
>
> I am curious, how do you think AMD CodeAnalyst works in regards to
> performance counting?  It seems to be quite fast to me, only causing a
> slow-down of between 2x to 6x depending on the program.
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-- 
Giri