Pandas: filter data frame based on percentile condition

I have a data frame df with some basic web stats ranked by Page Views (PVs):

URL  PVs
1    1500
2    1200
3    900
4    700
:
100  25

I am trying to filter and count number of URLs which contribute different percentile of page views (PVs). Say, I want to know how many and which once URLs brought 90% of PVs (or 10%).

I calculated percentiles:

df.quantile(np.linspace(.1, 1, 9, 0))

And I know I can iterate through rows like this (so I can sum them up):

for index, row in df.iterrows():
    print row['PVs']

But I cannot figure out how to stop when a certain threshold is reached. Will appreciate your help!