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/dev/cpuid or /proc/cpuinfo

To: Linux MIPS <linux-mips@linux-mips.org>
Subject: /dev/cpuid or /proc/cpuinfo
From: Philip Mucci <mucci@cs.utk.edu>
Date: Mon, 30 Jan 2006 18:54:29 +0000
In-reply-to: <Pine.LNX.4.44.0601271349350.2185-100000@bharathi.midascomm.com>
Organization: Innovative Computing Laboratory
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <Pine.LNX.4.44.0601271349350.2185-100000@bharathi.midascomm.com>
Sender: linux-mips-bounce@linux-mips.org
Hello MIPSers,

In reference to the performance counting thread we had going earlier,
I've noticed a 'feature' I need out of MIPS/Linux that isn't currently
available. This has also recently come up on the oprofile list with one
of the oprofile/mips tools not being able to grab cpu Mhz
from /proc/cpuinfo because it's not there.

I have need to execute the mfc0 instruction on the config register and
grok the results to find out things like cache size etc. In addition, it
might be nice to also actually be able to find out the clock rate.
(Currently I grab BogoMIPS and punt.)

On the intel and PPC systems, I believe you can execute similar
instructions from user mode which makes things easy. However, of course
an MFC0 is a privileged instruction...meaning that if the value or
values aren't found in /proc/cpuinfo, I'm s.o.l.

What does the list think about this? Making a mips /dev/cpuid is a bit
gross but extending and grokking /proc/cpuinfo is perhaps grosser...and
many tools do just this (like PAPI and oprofile's opreport...)

Comments? I'm certainly willing to implement this, but I'd rather 'do it
right the first time' rather than get rotten vegetables thrown my way.

Phil





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