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". -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
