Subject: Re: SATA_SIL works with 2.6.7-bk8 seagate drive, but oops
From: Albert Cahalan <albert@users.sf.net>
To: linux-kernel mailing list <linux-kernel@vger.kernel.org>
Cc: george@galis.org, Linus Torvalds <torvalds@osdl.org>
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Date: 26 Jun 2004 08:37:10 -0400
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Linus Torvalds writes:
> On Fri, 25 Jun 2004, George Georgalis wrote:

>> Could this be related to "Unknown HZ value! (91) Assume 100." which
>> started showing up with VIA motherboards on 2.5.x (I think) on top or ps
>> commands.  When I researched it before, It never caused ill, had been
>> identified as a "kernel bug" but benign. I know nothing more.
>
> No, that's just a pstools bug. It shouldn't try to guess HZ at all.

With an older kernel I'd say he's losing 9% of his clock ticks.
In this case though, incompatible /proc/stat changes are
at fault. No longer does idle CPU time include IO-wait CPU time.
This shouldn't have changed; user tools can subtract as needed.

I'm sorry to say that the HZ-guessing code is now only
used for the 2.2.xx kernels. Over the years it has found
many clock problems. Had the 2.4.xx kernels used a 64-bit
jiffies counter, the HZ-guessing code would still be used.

You never did come up with an alternative to HZ-guessing
that would work on those old 1200-HZ Alpha boxes, the ARM
boxes that ran at 64 HZ and so on. I suppose you can blame
the arch maintainers, but user-space has to deal with it.
So HZ-guessing is a workaround for a kernel bug, especially
because you claim that HZ (USER_HZ now) is part of the ABI.


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