linux-kernel - Re: [PATCH v4 2/2] perf x86: Exposing an Uncore unit to PMON for Intel Xeon® server platform

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Date:   Tue, 21 Jan 2020 19:15:56 +0300
From:   "Sudarikov, Roman" <roman.sudarikov@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        linux-kernel@...r.kernel.org, eranian@...gle.com,
        bgregg@...flix.com, kan.liang@...ux.intel.com,
        alexander.antonov@...el.com
Subject: Re: [PATCH v4 2/2] perf x86: Exposing an Uncore unit to PMON for Intel Xeon® server platform

On 17.01.2020 19:54, Greg KH wrote:
> On Fri, Jan 17, 2020 at 08:23:57AM -0800, Andi Kleen wrote:
>>> I thought I was nice and gentle last time and said that this was a
>>> really bad idea and you would fix it up.  That didn't happen, so I am
>>> being explicit here, THIS IS NOT AN ACCEPTABLE FILE OUTPUT FOR A SYSFS
>>> FILE.
>> Could you suggest how such a 1:N mapping should be expressed instead in
>> sysfs?
> I have yet to figure out what it is you all are trying to express here
> given a lack of Documentation/ABI/ file :)
>
> But again, sysfs is ONE VALUE PER FILE.  You have a list of items here,
> that is bounded only by the number of devices in the system at the
> moment.  That number will go up in time, as we all know.  So this is
> just not going to work at all as-is.
>
> greg k-h

Hi Greg,

Technically, the motivation behind this patch is to enable Linux perf tool
to attribute IO traffic to IO device.

Currently, perf tool provides interface to configure IO PMUs only 
without any
context.

Understanding IIO stack concept to find which IIO stack that particular
IO device is connected to, or to identify an IIO PMON block to program
for monitoring specific IIO stack assumes a lot of implicit knowledge
about given Intel server platform architecture.


Please consider the following mapping schema:

1. new "mapping" directory is to be added under each uncore_iio_N directory
2. that "mapping" directory is supposed to contain symlinks named "dieN"
which are pointed to corresponding root bus.
Below is how it looks like for 2S machine:

# ll uncore_iio_0/mapping/
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die0 -> 
../../pci0000:00/pci_bus/0000:00
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die1 -> 
../../pci0000:80/pci_bus/0000:80

# ll uncore_iio_1/mapping/
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die0 -> 
../../pci0000:17/pci_bus/0000:17
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die1 -> 
../../pci0000:85/pci_bus/0000:85

# ll uncore_iio_2/mapping/
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die0 -> 
../../pci0000:3a/pci_bus/0000:3a
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die1 -> 
../../pci0000:ae/pci_bus/0000:ae

# ll uncore_iio_3/mapping/
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die0 -> 
../../pci0000:5d/pci_bus/0000:5d
lrwxrwxrwx 1 root root 0 Jan 20 23:55 die1 -> 
../../pci0000:d7/pci_bus/0000:d7


Thanks,
Roman