Re: [Perfctr-devel] RE: [perfmon] Re: quick overview of the

Bryan O'Sullivan
2006-01-25T22:46:43Z

On Wed, 2006-01-25 at 14:28 -0800, Stephane Eranian wrote:

> So it would help if you could
> name the extended features you referring to.

I'm dubious about the hands-off buffer format in general. Does this
mean that userspace needs to modprobe a specific set of modules in order
to do normal sampling? If so, how do you work around the need for users
to be root in order to use these interfaces?

> And perfmon
> does allow it to continue working using almost all of its kernel code.
> This is leveraging the custom sampling buffer format support in perfmon.
> So you can say this is an extended feature that adds complexity.
> But OTOH, this is one elegant way of supporting an existing interface
> without breaking all the tools.

So are you saying that part of the existing oprofile code can be deleted
if perfmon is merged, and that userspace won't notice?

> We were able to proide this support
> with a few hundred lines of code without hacking the regular sampling
> format. Instead we simply created a dedicated PEBS format as a kernel module.

Does this mean I can't sample the PMCs on a P4 if I don't have the
special PEBS module loaded? Do I need to be root to do that?

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