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

[Suravee Suthikulpanit]

On 02/23/2016 12:24 PM, Alex Williamson wrote:
> On Tue, 23 Feb 2016 12:12:42 +0700
> Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx> wrote:
>
> > 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.
>
> We already expose individual IOMMU hardware units in /sys/class/iommu/,
> you might consider trying to match the names there for the convenience
> of the user.  Looks like we use ivhd%d for AMD.  Thanks,
>
> Alex

Hm, the PMU for AMD IOMMU is currently shown as /sys/device/amd_iommu. I 
am not sure if /sys/device/ivhd[0|1|...] would be obvious to users that 
IVHD is really the AMD IOMMU.

Suravee