Re: [Perfctr-devel] [perfmon] 2.6.17.1 new perfmon code base, libpfm,

[William Cohen <wcohen@redhat.com>]

Stephane Eranian wrote:
> Will,
> 
> On Fri, Jun 23, 2006 at 05:13:47PM -0400, William Cohen wrote:
> 
>>Hi Stephane,
>>
>>Some quick questions about the current perfmon code.
>>
>>
>>The athlon has very similar hw to the amd64 and there is now 32-bit
>>x86-64 support. Wouldn't it make sense to move perfmon_amd.c to i386
>>and have it work in the same way as perfmon_p4.c does currently for p4
>>and em64t?
>>
> 
> Does Athlon have 4 counters as well. I don't have the HW so I cannot really
> test. I suspect they are similar. If you have HW and you can test, I don't
> have a problem.

I have an Athlon machine in the office that I can test this change out 
on and send you a diff.

>>Could the 32-bit and 64-bit code be combined in a manner similar to
>>oprofile and avoid duplication between perfmon_em64t_pebs.c and
>>perfmon_p4_pebs.c?  pfm_{p4|em64}_ds_area and
>>pfm_{p4|em64t}_pebs_sample_entry have differences due to the upgrade
>>from 32 to 64 bit values.
>>
> 
> You have several issues here:
> 	- the 64-bit version has 8 more reigsters int the PEBS entry
> 	- the PEBS entry uses 32 or 64 bitfields depending on data model
> 	- the ds_area uses 32 or 64 bits depending on the data model except for the threshold value
> 
> Now remember that on on EM64T we also support 32-bit (i386) binaries. 
> With an EM64T kernel you would have the 64-bit PEBS format. With the same UUID if would satisfy
> a i386 binary and this is wrong because they would not match the definition of the PEBS entry.
> We need to keep the PEBS 32 and 64-bit format UUIDs different. At the source code level, you would
> need to ifdef __x86_64__ and __i386__ to switch struct definition and UUID. That's doable but is
> this clean?

Certainly given the differences in the pebs elements there will need to 
unique names for each. It was just a thought to factor out the similar code.

There is support to handle amd64 hardware running on 32-bit kernel. Has 
someone verified that the em64t processor generate 32-bit compatible 
entries when running in 32-bit mode? Or does it always write out 64-bit 
style PEBS entries?

>>Why isn't Intel family 0xf model 3 not supported?
>>	Model 1,2, 4, and 5 are supported.
>>	Model 3 Pentium4 isn't that different is it?
> 
> 
> I have not looked at this. I don't have a lot of P4 HW. I think that
> all family 15 uses the same PMU. Could someone confirm this?

A NC State University professor mentioned that the ommission of model 3 
was a problem because his machine were model 3. I suggested the addition 
of case for model 3 processors to get him going on that.

-Will