Re: [Perfctr-devel] Re: [perfmon] perfmon2 code review: 32-bit ABI on 64-bit OS

[Eric Gouriou <eric.gouriou@hp.com>]

David Gibson wrote:
> On Sat, Feb 11, 2006 at 02:33:54PM -0800, Stephane Eranian wrote:
[...]
>> The most challenging piece is the IP (program pointer) that is in every
>> sample. Today it is defined as unsigned long because this is fairly
>> natural for a code address. The 64bit OS captures addresses as 64-bit,
>> the 32-bit monitoring tool running on top has to consume them as 64-bit
>> addresses, so u64 would be fine. 
>>
>> But not on a 32-bit kernel with a 32-bit tool, addresses exported as u64
>> would certainly work but consume double to buffer space, and that is a
>> more serious issue in my mind.
> 
> Hmm.. does the sampling buffer collect on userspace PC values, or
> kernel ones as well?

  Either, or both, depending on the measurement settings.

  I live in a 64-bit world, so my take on this issue would be to expose
the PC as a uint64_t, always. There is already so much overhead in the
default per-sample header that I wouldn't worry about it.

  Now 64 bit might not always be enough. E.g., on PA-RISC. But _I_ do
not care much about Linux on PA.

   Eric

-- 
Eric Gouriou                                         eric.gouriou@hp.com