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

[Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx>]

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?

> > 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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