On Wed, Sep 17, 2014 at 08:01:08AM -0400, Peter Hurley wrote: > On 09/16/2014 04:50 AM, Frans Klaver wrote: > > On Mon, Sep 15, 2014 at 01:31:56PM -0400, Peter Hurley wrote: > >> On 09/15/2014 11:39 AM, Peter Hurley wrote: > >>> On 09/15/2014 10:00 AM, Frans Klaver wrote: > >>>> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart > >>>> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces > >>>> this to about 170 overflows in 10 minutes. > >>> > >>> Why is the threadirqs kernel boot option not sufficient? > >>> Or conversely, shouldn't this be selectable? > >> > > > > I wasn't aware of the threadirqs boot option. I also wouldn't know if > > this should be selectable. What would be a reason to favor the > > non-threaded irq over the threaded irq? > > Not everyone cares enough about serial to dedicate kthreads to it :) Fair enough. In that light, we might not care enough about other subsystems to dedicate kthreads to it :). Selectable seems reasonable in that case. > >> Also, do you see the same performance differential when you implement this > >> in the 8250 driver (that is, on top of Sebastian's omap->8250 conversion)? > >> > > > > I haven't gotten Sebastian's driver to work properly yet on the console. > > There was no reason for me yet to throw my omap changes on top of > > Sebastian's queue. > > > >>> PS - To overflow the 64 byte RX FIFO at those data rates means interrupt > >>> latency in excess of 250us? > > > > At 3686400 baud it should take about 174 us to fill a 64 byte buffer. I > > haven't done any measurements on the interrupt latency though. If you > > consider that we're sending about 1kB of data, 240 times a second, we're > > spending a lot of time reading data from the uart. I can imagine the > > system has other work to do as well. > > System work should not keep irqs from being serviced. Even 174us is a long > time not to service an interrupt. Maybe console writes are keeping the isr > from running? That's quite possible. I'll have to redo the test setup I had for this to give you a decent answer. I'll have to do that anyway as Sebastian's 8250 conversion improves. Thanks for the comments, Frans -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
