On Fri, Jul 15, 2016 at 01:38:12PM +0300, Felipe Balbi wrote: > > Hi, > > Bin Gao <bin.gao@xxxxxxxxxxxxxxx> writes: > > +static void print_message(int port, bool is_cmsg, u8 msg, bool recv) > > +{ > > + pr_info("sink port %d: %s message %s %s\n", port, > > + is_cmsg ? "Control" : "Data", > > + msg_to_string(is_cmsg, msg), > > + recv ? "received" : "sent(wait GOODCRC)"); > > +} > > this is problematic. By default, we're all using 115200 8N1 baud > rate. This message alone prints anywhere from 50 to 100 characters (I > didn't really count properly, these are rough numbers), and that takes: > > n50chars_time = 50 / (115200 / 10) = 4.3ms > n100chars_time = 100 / (115200 / 10) = 8.6ms > > Considering you have 30ms to reply with Power Request after GoodCRC, and > considering you're printing several of these messages, they become > really expensive and eat up valuable time from tSenderReply. printk() should be async, so it shouldn't be that big of a deal. What is wrong is that this isn't using dev_info(). > This should really be a pr_debug() or, better yet, a tracepoint. Yes, that would be best (dev_dbg() or a tracepoint.) thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html