dtrace discuss - Jun 2009 - does dtrace uses any special hardware for tracing

I am new-bie in this world of unix..
just wanted to know that if DTrace uses any hardware support for its function.

thanks in advance
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Hello!

On Sat, Jun 20, 2009 at 7:57 PM, Pankaj<me.pankajparakh at gmail.com>
wrote:
> I am new-bie in this world of unix..
> just wanted to know that if DTrace uses any hardware support for its
function.
The "closest" thing to hardware that the  DTrace framework needs is
appropriate software support in the Kernel. So, the answer is No. I
might be wrong here, though.

HTH,
Amit
>
> thanks in advance
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Pankaj wrote:
> I am new-bie in this world of unix..
> just wanted to know that if DTrace uses any hardware support for its
function.
> 
> thanks in advance
No, DTrace doesn''t require any hardware support. Just to help clarify, 
DTrace is an observability framework that allows you to trace software 
events. ''Events'' is a pretty generic word in this context, but
the cool
thing is that DTrace allows you to observe any kind of event. From core 
kernel events (for instance, scheduling or virtual memory events), to 
syscalls, library routines, user land code, ... everything.

So it''s all in the software, no hardware needed.

Hope that helps.

Rafael

I too had the same intuition that DTrace works completely in software, but after
knowing that there is Performance Monitoring Unit(PMU) present in
intel''s chip, so I got confused if DTRace uses it, also same type of
hardware is present in AMD''s chip. I might be wrong.

Need conformation.
-- 
This message posted from opensolaris.org

On 6/20/09, Pankaj <me.pankajparakh at gmail.com>
wrote:
> I too had the same intuition that DTrace works completely in software
DTrace works by dynamically patching the text (the instructions) to
pass control to the DTrace framework. This is how DTrace gets zero
overhead when the probe is not turned on.

> but after knowing that there is Performance Monitoring Unit(PMU) present in
intel''s chip, so I got confused if DTRace uses it, also same type of
hardware is present in AMD''s chip.
Hardware performance counter support was added to profile processor
level events like cache miss, instruction retired, etc. You can take a
look at this page for details:

http://blogs.sun.com/jonh/entry/finally_dtrace_meets_the_cpu

Rayson



> I might be wrong.
>
> Need conformation.
> --
> This message posted from opensolaris.org
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> dtrace-discuss mailing list
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>

Pankaj wrote:
> I too had the same intuition that DTrace works completely in software, but
after knowing that there is Performance Monitoring Unit(PMU) present in
intel''s chip, so I got confused if DTRace uses it, also same type of
hardware is present in AMD''s chip. I might be wrong.
>   
  The intel/amd microprocessors provide acess to performance counters 
which can be programmed to gather information about
  hardware events like number of instructions executed, number of cache 
misses ...
  The ''cpc'' provider in DTrace makes  available probes which
are
associated to  these performance counters.
  More details at:
    http://wikis.sun.com/display/DTrace/cpc+Provider

Pramod

 
> Need conformation.
>

>> I too had the same intuition that DTrace works completely in software, 
>> but after knowing that there is Performance Monitoring Unit(PMU) 
>> present in intel''s chip, so I got confused if DTRace uses it,
also
>> same type of hardware is present in AMD''s chip. I might be
wrong.
>>   
> 
>  The intel/amd microprocessors provide acess to performance counters 
> which can be programmed to gather information about
>  hardware events like number of instructions executed, number of cache 
> misses ...
>  The ''cpc'' provider in DTrace makes  available probes
which are
> associated to  these performance counters.
>  More details at:
>    http://wikis.sun.com/display/DTrace/cpc+Provider
I''m sure Pramod was just citing Intel/AMD as that was in the
original question but just to be clear; the cpc provider gives
access to the performance counters on any platform that Solaris
runs on**.

Jon.

** Apart from the old USI/II processors as the performance counter
back-end doesn''t provide a counter overflow mechanism. However, if
you''re doing performance analysis on one of these processors,
you''ve
got *way* bigger problems than that...

Pankaj wrote:
> I too had the same intuition that DTrace works completely in software, but
after knowing that there is Performance Monitoring Unit(PMU) present in
intel''s chip, so I got confused if DTRace uses it, also same type of
hardware is present in AMD''s chip. I might be wrong.
> 
> Need conformation.
Well, it uses the features of the CPUs it runs on, like breakpoint 
instructions, traps, etc., but it''s not *special* hardware of any sort;
it''s just the standard hardware you get with your computer.