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

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Date:	Tue, 23 Feb 2016 16:56:22 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	<iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<acme@...nel.org>, <andihartmann@...enet.de>, <mingo@...hat.com>,
	<bp@...en8.de>
Subject: Re: [PATCH V4 5/6] perf/amd/iommu: Enable support for multiple IOMMUs



On 02/23/2016 12:24 PM, Alex Williamson wrote:
> On Tue, 23 Feb 2016 12:12:42 +0700
> Suravee Suthikulpanit <Suravee.Suthikulpanit@....com> 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