Re: [patch] i386: avoid expensive ppro ordering workaround for default 686 kernels

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

> Hmm, I don't understand what you mean. Obviously other busmasters aren't
> participating in any locking or smp_*mb() ordering protocols.

The unlock paths are visible to busmasters

		write to DMA buffer
		unlock
can turn into

		unlock
		write to DMA buffer

Whether that actually matters in any code we have I don't know.

> > - re-order the assumed processor generations supported to put VIA C3/C5
> > above Preventium Pro
> 
> Adrian Bunk's patch to make each CPU type explicitly selectable IMO is the
> best way to do this.

If you get to pick the combination you want then yes.

> > to 586 < 686 < PPro < C3 < PII < ...
> > 
> > then selecting VIA C3 support will get you a kernel with the properties
> > all the distribution vendors want for their higher end mainstream kernel -
> > "runs on modern systems".
> 
> I don't agree. If we support those options, we should support them properly.
> And if you build an SMP kernel for a 586 for example, you should not get lumped
> with those pentiumpro workarounds.

The cost on a 586 SMP box (ie pentium) is basically nil. All cross CPU
transactions are hideously slow anyway locked or not. On a PII or later I
agree entirely you don't want them by default.

Alan

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