Pin Data is very slow at iphone 5

When i try to use the ParseObject to store the local data, i find that the performance is very bad, when i execute below codes at IOS 5, will take about 1 - 2 secs for every loop. But seems that the performance is ok at emulator and iphone 5s.

for(int i = 0; i < 20; i++){
    PFObject *pfObj = [PFObject objectWithClassName:@"TestStore"];

    pfObj[@"TestStore_ID"] = userId;

    pfObj[@"TestStore_URL"] = avatarUrl;

    [pfObj pinWithName:@"TestStore"];

}