Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table

Avi Kivity
2011-06-29T12:18:59Z

On 06/29/2011 02:50 PM, Xiao Guangrong wrote:
> >> >
> >> > I think we should do this unconditionally. The cost of ping-ponging the shared cache line containing reader_counter will increase with large smp counts. On the other hand, zap_page is very rare, so it can be a little slower. Also, less code paths = easier to understand.
> >> >
> >>
> >> On soft mmu, zap_page is very frequently, it can cause performance regression in my test.
> >
> > Any idea what the cause of the regression is? It seems to me that simply deferring freeing shouldn't have a large impact.
> >
>
> I guess it is because the page is freed too frequently, i have done the test, it shows
> about 3219 pages is freed per second
>
> Kernbench performance comparing:
>
> the origin way: 3m27.723
> free all shadow page in rcu context: 3m30.519

I don't recall seeing such a high free rate. Who is doing all this zapping?

You may be able to find out with the function tracer + call graph.

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error compiling committee.c: too many arguments to function