Re: Entering C3 Processor State without a Bus Arbiter

[Dominik Brodowski <linux-X3ehHDuj6sIIGcDfoQAp7BvVK+yQ3ZXh@public.gmane.org>]

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On Thu, Jan 15, 2004 at 03:52:12PM -0800, Nate Lawson wrote:
> > After removing the restrictions in the source files, and adding a WBINVD
> > instruction right before the read from P_LVL3 - the processor was put in
> > the C3 state. This is on my Via Apollo Pro133A based Abit VP6 board,
> > which does not have a Bus Arbiter. Just for the record, I did pull out
> > the second CPU, so I can do "safer" experimentation.
> 
> WBINVD is too expensive when you're entering C3 hundreds of times per
> second.  Try playing back an mp3 while dd'ing a CDROM in PIO mode to your
> hard drive.  Goodbye data, hello backups!  The CPU can't snoop the bus in
> C3.

You shouldn't enter C3 at all when the CPU is woken up hundreds of times per
second. Maximum allowed latency is 1ms, IIRC -- you really shouldn't get
into this state while dd'ing a CDROM or something else...

Problem is, WBINVD might take even longer than 1ms, even though the maximum
I got on my PIII notebook was about 900us...

	Dominik

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