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From: Greg KH <gregkh@linuxfoundation.org>
To: roman.sudarikov@linux.intel.com
Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
	mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
	jolsa@redhat.com, namhyung@kernel.org,
	linux-kernel@vger.kernel.org, eranian@google.com,
	bgregg@netflix.com, ak@linux.intel.com,
	kan.liang@linux.intel.com, alexander.antonov@intel.com
Subject: Re: [PATCH v4 2/2] perf x86: Exposing an Uncore unit to PMON for Intel Xeon® server platform
Date: Fri, 17 Jan 2020 15:19:44 +0100	[thread overview]
Message-ID: <20200117141944.GC1856891@kroah.com> (raw)
In-Reply-To: <20200117133759.5729-3-roman.sudarikov@linux.intel.com>

On Fri, Jan 17, 2020 at 04:37:59PM +0300, roman.sudarikov@linux.intel.com wrote:
> From: Roman Sudarikov <roman.sudarikov@linux.intel.com>
> 
> Current version supports a server line starting Intel® Xeon® Processor
> Scalable Family and introduces mapping for IIO Uncore units only.
> Other units can be added on demand.
> 
> IIO stack to PMON mapping is exposed through:
>     /sys/devices/uncore_iio_<pmu_idx>/mapping
>     in the following format: domain:bus
> 
> For example, on a 4-die Intel Xeon® server platform:
>     $ cat /sys/devices/uncore_iio_0/mapping
>     0000:00,0000:40,0000:80,0000:c0

Again, horrible format, why do we have to parse this in userspace like
this?  Who will use this file?  What do they really need?

And what happens when you have too many "dies" in a system and you
overflow the sysfs file?  We have already seen this happen for other
sysfs files that assumed "oh, we will never have that many
cpus/leds/whatever in a system at one time" and now they have to go do
horrid hacks to get around the PAGE_SIZE limitation of sysfs files.

DO NOT DO THIS!

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.

greg k-h

  reply	other threads:[~2020-01-17 14:19 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-17 13:37 [PATCH v4 0/2] perf x86: Exposing IO stack to IO PMON mapping through sysfs roman.sudarikov
2020-01-17 13:37 ` [PATCH v4 1/2] perf x86: Infrastructure for exposing an Uncore unit to PMON mapping roman.sudarikov
2020-01-17 14:16   ` Greg KH
2020-01-17 13:37 ` [PATCH v4 2/2] perf x86: Exposing an Uncore unit to PMON for Intel Xeon® server platform roman.sudarikov
2020-01-17 14:19   ` Greg KH [this message]
2020-01-17 16:23     ` Andi Kleen
2020-01-17 16:54       ` Greg KH
2020-01-17 17:27         ` Andi Kleen
2020-01-17 18:42           ` Greg KH
2020-01-17 19:12             ` Andi Kleen
2020-01-17 23:03               ` Greg KH
2020-01-17 23:21                 ` Andi Kleen
2020-01-21 16:15         ` Sudarikov, Roman
2020-01-21 17:15           ` Greg KH
2020-01-28 14:55             ` Sudarikov, Roman
2020-01-28 20:19               ` Liang, Kan
2020-01-17 14:14 ` [PATCH v4 0/2] perf x86: Exposing IO stack to IO PMON mapping through sysfs Greg KH

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