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Re: [Xen-devel] vnif socket buffer mistaken for pagetable page causes major performance problem





Gianluca Guida wrote:
Herbert van den Bergh wrote:
Can you be a little more specific about what is the performance loss,
Network throughput was reduced to 10% of normal.
in what workload,
A network send throughput test using netperf.

This is with a Linux guest (HVM of course), right?

Right.

and what heuristic you found to be wrong in this case?
The access pattern to the memory page that was recognized as a pagetable access was a regular memcpy doing 4 byte aligned writes into a newly allocated page. I'm not that familiar with the shadow pagetable code, so I don't know how "wrong" this is, just that it caused a false positive on this type of memory access.

Most probably the guest OS is recycling a page that used to be a pagetable and that is still shadowed.

Thanks,
Gianluca

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