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

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Date:	Mon, 22 Feb 2016 15:07:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	joro@...tes.org, bp@...en8.de, mingo@...hat.com, acme@...nel.org,
	andihartmann@...enet.de, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH V4 5/6] perf/amd/iommu: Enable support for multiple IOMMUs

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 ?