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

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Date:	Tue, 23 Feb 2016 12:12:42 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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

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