linux-kernel - RE: [GIT PULL] Additional x86 fixes for 2.6.31-rc5

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Date:	Thu, 6 Aug 2009 07:10:00 +0800
From:	"Tan, Wei Chong" <wei.chong.tan@...el.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	John Stultz <johnstul@...ibm.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: RE: [GIT PULL] Additional x86 fixes for 2.6.31-rc5

> Sure, we might want the error term to be even smaller, but 
> in no way does it actually invalidate any of the logic - 
> the 'tsc' reading is just a guess anyway. Also, I think 
> that the real issue isn't even an SMI - but the fact that 
> in the very last iteration of the loop, there's no 
> serializing instruction _after_ the last 'rdtsc'. So even 
> in the absense of SMI's, we do have a situation where the 
> cycle counter was read without proper serialization.
> 

Hi,

I just recall something which I cannot understand.  Earlier when we observed the wrong CPU frequency phenomenon (1666MHz being identified as 1800MHz), we use the same CPU and put them on 2 different boards.  On one board, the failure rate is high (about 1 out of every 20).  On the other, it almost never fails.
We compare the 2 boards and they are quite close to each other with one very prominent difference.  The failing board has no PS/2 port and so is using all USB keyboard/mouse while the good board uses PS/2 keyboard/mouse.
Thus, we plug in a USB keyboard on the good board and were then able produce the failure on the good board (despite at a lower failure rate, 1 out of every 100).
Does this not point to SMI?

Regards,
Wei Chong.
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