Messages in this thread | | | Date | Wed, 29 Jun 2011 20:28:37 +0800 | From | Xiao Guangrong <> | Subject | Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table |
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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".
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