Re: [PATCH V4 5/6] perf/amd/iommu: Enable support for multiple IOMMUs

[Suravee Suthikulpanit]

Hi

On 02/22/2016 09:07 PM, Peter Zijlstra wrote:
> On Mon, Feb 22, 2016 at 03:00:31PM +0700, Suravee Suthikulpanit wrote:
> > > So I really don't have time to review new muck while I'm hunting perf
> > > core fail, but Boris made me look at this.
> > >
> > > This is crazy, if you have multiple IOMMUs then create an event per
> > > IOMMU, do _NOT_ fold them all into a single event.
> >
> > These are system-wide events, which are programmed on every IOMMU the same
> > way. I am not sure what you meant by creating an event per IOMMU. Do you
> > mean I should create internal per-IOMMU struct perf_event for each event?
>
> No, I meant to expose each IOMMU individually to userspace, as a
> separate device.
>
> Is there never a case to profile just one of the IOMMUs ?

I see. That's definitely doable and simpler to implement.

I was not sure if making users specify the IOMMU instance (e.g. 
amd_iommu_0/<ev name> , amd_iommu_1/<ev_name>, ....) would be too 
tedious. However, this would actually give users better control of the 
performance events, which is a good trade-off. I think it is acceptable.

I'll make the change and send this out in V5.

Thanks,
Suravee