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    SubjectRe: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table
    On 06/29/2011 03:28 PM, Xiao Guangrong wrote:
    > On 06/29/2011 08:18 PM, Avi Kivity wrote:
    > > 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.
    > >
    >
    > I looked into it before, it is caused by "write flood" detected, i also noticed
    > some pages are zapped and allocation again and again, maybe we need to improve
    > the algorithm of detecting "write flood".

    Ok. Let's drop the two paths, and put this improvement on the TODO instead.

    --
    error compiling committee.c: too many arguments to function



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