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From: Ralf Baechle <ralf@linux-mips.org>
To: Earl Chew <echew@ixiacom.com>
Cc: linux-mips@linux-mips.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Publishing mips_hpt_frequency in /proc/cpuinfo
Date: Fri, 28 Jan 2011 11:57:20 +0100	[thread overview]
Message-ID: <20110128105720.GA28544@linux-mips.org> (raw)
In-Reply-To: <4D424D4B.5090002@ixiacom.com>

On Thu, Jan 27, 2011 at 08:59:55PM -0800, Earl Chew wrote:

> The CPU frequency is known to the Linux kernel. For example:
> 
> > CPU revision is: 00019374 (MIPS 24Kc)
> > Atheros AR7161 rev 2, CPU:680.000 MHz, AHB:170.000 MHz, DDR:340.000 MHz
> > ...
> > Calibrating delay loop... 452.19 BogoMIPS (lpj=2260992)
> 
> Unfortunately that information is not available from userspace:
> 
> > cpu model               : MIPS 24Kc V7.4
> > BogoMIPS                : 452.19
> 
> This makes it difficult to use CPU timers (rdhwr) from user space
> applications.
> 
> 
> Is there any reason not to publish mips_hpt_frequency in /proc/cpuinfo ?

The CPU clock frequency may change at any time due to clockscaling  A
process might be rescheduled to another CPU running at a different clock
rate.  A suspended process might miss counter wraparounds.

This right approach is to handle this in a virtual syscall, something like
vsys_clock_gettime().

  Ralf

  parent reply	other threads:[~2011-01-28 10:57 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-28  4:59 Publishing mips_hpt_frequency in /proc/cpuinfo Earl Chew
2011-01-28  4:59 ` Earl Chew
2011-01-28 10:57 ` Ralf Baechle [this message]
2011-01-28 12:28   ` Thomas Gleixner
2011-01-28 15:29     ` Earl Chew

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