linux-kernel - Re: [PATCH] arch/tile: add /proc/tile, /proc/sys/tile, and a sysfs cpu attribute

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Date:	Fri, 20 May 2011 16:37:20 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch/tile: add /proc/tile, /proc/sys/tile, and a sysfs cpu attribute

On Friday 20 May 2011 16:26:57 Chris Metcalf wrote:
> >>>> /proc/tile/hardwall
> >>>>   Information on the set of currently active hardwalls (note that
> >>>>   the implementation is already present in arch/tile/kernel/hardwall.c;
> >>>>   this change just enables it)
> >> This one is not a hypervisor-related file.  It just lists information about
> >> the set of Linux hardwalls currently active.  Again, it's not primarily
> >> intended for programmatic use, but as a diagnostic tool.
> > same here, I'd still put it into the hypervisor structure.
> 
> Since /proc/tile/hardwall has no connection to the hypervisor whatsoever,
> I'm reluctant to put it under /sys/hypervisor.

Ah, I see. I didn't notice that it was in the other file. You are
absolutely right, this does not belong into /sys/hypervisor and
fits well into procfs, we just need to find the right place.

> Perhaps in this case it would be reasonable to just have the hardwall
> subsystem put the file in /proc/driver/hardwall, or even /proc/hardwall? 
> Or I could make the /dev/hardwall char device dump out the ASCII text that
> we currently get from /proc/hardwall if you read from it, which is a little
> weird but not inconceivable.  For example it currently shows things like this:
> 
> # cat /proc/tile/hardwall
> 2x2 1,1 pids: 484@2,1 479@1,1
> 2x2 0,3 pids:
> 
> In this example "2x2 1,1" is a 2x2 grid of cpus starting at grid (x,y)
> position (1,1), with task 484 bound to the cpu at (x,y) position (2,1).

Any chance you can still restructure the information? I would recommend
making it a first-class procfs member, since the data is really per-task.

You can add a conditional entry to tgid_base_stuff[] in fs/proc/base.c
to make it show up for each pid, and then just have the per-task information
in there to do the lookup the other way round:

# cat /proc/484/hardwall
2x2 1,1 @2,1

# cat /proc/479/hardwall
2x2 1,1 @1,1

	Arnd
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