Hello,
On Mon, Jan 08, 2007 at 01:17:40PM -0800, Stephane Eranian wrote:
> This little exercise raised a few questions:
>
> - the code that uses the v2.3 interface (for all architectures) now relies
> on libpfm. You pass to pfm_dispatch_events() OProfile event names. So
> that assumes that OProfile and libpfm events match. I am not sure this
> is the case for all events on all x86 processors. We need to solve this.
>
After taking a closer look, I came to the conclusion that we cannot use
libpfm to do the event assignment. There are several complictaed issues
related to:
1/ Event names
OProfile and libpfm may not use the same exact name for the same
event.
Finding an event in libpfm is based upon string matching.
2/ Handling of unit masks
In OProfile unit masks are provide using an hexadecimal bitmask.
In libpfm, they are provided using a string.
Reconciling both of those would require a lot of work.
An alternative is to let OProfile manage names and unit masks and have
the daemon simply manage the mapping of OProfile counter indexes to
perfmon counter indexes. Such mapping is trivial for many processors.
It is more difficult for the P4. This approach is fairly similar to what
we have today for OProfile on IA-64.
--
-Stephane
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