Re: [Xen-devel] [PATCH] xen/domctl: lower loglevel of XEN_DOMCTL_memory_mapping

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.15 at 02:59, <konrad.wilk@xxxxxxxxxx> wrote:
> If you want a formula I would do:
> 
> #define MAX_SOCKETS 8
> 
>  max_pfns = pow(2,(MAX_SOCKETS - (max(nr_iommus(), MAX_SOCKETS)))) * 64;
> 
> Where nr_iommus would have to be somehow implemented, ditto for pow.
> 
> This should give you:
>  8    -> 64
>  7    -> 128
>  6    -> 256
>  5    -> 512
>  4    -> 1024
>  3    -> 2048
>  2    -> 4096
>  1    -> 16384

16k seems excessive as a default. Also - why would this be related
to the number of sockets? I don't think there's a one-IOMMU-per-
socket rule; fixed-number-of-IOMMUs-per-node might come closer,
but there we'd have the problem of what "fixed number" is. Wouldn't
something as simple as 1024 / nr_iommus() do?

I also don't follow what cache flushes you talked about earlier: I
don't think the IOMMUs drive any global cache flushes, and I
would have thought the size limited IOTLB and (CPU side) cache
ones should be pretty limited in terms of bus load (unless the TLB
ones would get converted to global ones due to lacking IOMMU
capabilities). Is that not the case?

Jan


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