Re: MSI to memory?

[Zwane Mwaikambo]

On Wed, 7 Jul 2004, Helge Hafting wrote:

> Davide Rossetti wrote:
>
> > Rajesh Shah wrote:
> >
> >> What type of usage model did you have in mind to have the
> >>
> >> device write to memory instead of using MSI for interrupts?
> >>
> >>
> > for instance for a fast wake-up trick. the driver loops on a memory
> > location until the MSI write access changes the memory content...
>
> Won't that put a bad load on the bus?  Someone else might need it:
> * Another cpu in a smp system
> * Any device doing bus-master transfers, even in a UP system
>
> That polling loop had better be guaranteed to be _very_ short.

mwait/monitor is best suited for such things and doesn't result in
pounding on memory. Considering the box has MSI, there is a higher
possibility of it also having the mwait/monitor instructions.

	Zwane

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