Re: vnif socket buffer mistaken for pagetable page causes major performance problem

[Herbert van den Bergh <Herbert.van.den.Bergh@oracle.com>]

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