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Date: Wed, 17 Sep 2014 08:01:08 -0400 From: Peter Hurley <peter@...leysoftware.com> To: Frans Klaver <frans.klaver@...ns.com> CC: Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>, Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>, Mark Rutland <mark.rutland@....com>, Ian Campbell <ijc+devicetree@...lion.org.uk>, Kumar Gala <galak@...eaurora.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alexey Pelykh <alexey.pelykh@...il.com>, Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org, linux-omap@...r.kernel.org, devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 3/4] tty: omap-serial: use threaded interrupt handler 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 :) >> 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? Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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