linux-kernel - Re: [PATCH V3] x86, UV: BAU performance and error recovery

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Message-ID: <20100528233623.GA11356@sgi.com>
Date:	Fri, 28 May 2010 18:36:23 -0500
From:	Cliff Wickman <cpw@....com>
To:	Greg KH <gregkh@...e.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH V3] x86, UV: BAU performance and error recovery


On Fri, May 28, 2010 at 03:23:21PM -0700, Greg KH wrote:
> On Fri, May 28, 2010 at 02:43:35PM -0500, Cliff Wickman wrote:
> > 
> > On Fri, May 28, 2010 at 09:47:25AM -0700, Greg KH wrote:
> > > On Fri, May 28, 2010 at 09:30:25AM -0700, H. Peter Anvin wrote:
> > > > On 05/28/2010 06:33 AM, Cliff Wickman wrote:
> > > > > - adds modification of tuning variables through /proc/sgi_uv
> > > > 
> > > > Adding new directories in /proc for a proprietary architecture is
> > > > frowned upon, to put it mildly.  At the very least try to find a place
> > > > in sysfs for it.
> > > > 
> > > > [Cc: gregkh in order to find a place in sysfs]
> > > 
> > > Hm, what type of files are you needing here?  Do they corrispond with
> > > any specific hardware devices?  If so, just put them on the hardware
> > > devices in sysfs.
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > 
> > There is an SGI-specific directory in sysfs: /sys/firmware/sgi_uv
> > though the tuning variables for the handling of the hardware Broadcast
> > Assist Unit don't fit there very logically.  
> > 
> > The BAU's statistics are already displayed through the UV-only
> > /proc/sgi_uv/ptc_statistics.  This was deemed necessary because of the
> > potentially very large size of that file --- it is still true that a /sys file
> > is limited to one page, is it not?
> 
> It is limited to one single value, which would never be larger than a
> page, so yes, it is limited to one page.
> 
> What kind of information are you showing here?  Should this thing just
> be in debugfs instead?  You can do whatever you want there.
> 
> thanks,
> 
> greg k-h

/proc/sgi_uv/bau_tunables would be a read/write file to display and change
nine threshold and delay values for tuning the BAU driver.

I like debugfs, except that a distro may not build the kernel with it
configured on.  The tunables should be available as administrative
options on a customer kernel, not just as a development tool.

And in our case the distros are already building with other such writable
options in /proc/sgi_uv.  We'd like to postpone a wholesale move of such
options (assuming there will be some better place) and stay with the existing
location for this release.

I know we (the community) would like to move non-process info out of /proc.
It seems to me that we need a similar filesystem for large and/or 
administrative files.  That's my perspective.

-Cliff
-- 
Cliff Wickman
SGI
cpw@....com
(651) 683-3824
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