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SubjectRe: MSI to memory?
Roland Dreier wrote:

> Helge> Won't that put a bad load on the bus? Someone else might
> Helge> need it: * Another cpu in a smp system * Any device doing
> Helge> bus-master transfers, even in a UP system
>
>Actually with MSI, the PCI device writes directly to a host address.
>In the proposed usage in this mail thread, the address is in host
>memory, so there's no bus load to poll the memory. Presumably the
>memory will be pulled into cache for the duration of the poll loop, so
>there's not even any memory bandwidth consumed. (Of course this only
>works on an architecture where PCI DMA is cache coherent)
>
>
I see. Still, this should only be used when we expect a
short wait only, similiar to situations when we use a spinlock.
Otherwise, the cpu could be put to better use by scheduling.

Helge Hafting
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