Hello Manfred, On Monday 22 June 2015 10:20:10, Manfred Schlaegl wrote: > On 2015-06-22 08:48, Alexander Stein wrote: > > Am Samstag, 20. Juni 2015, 19:25:52 schrieb Manfred Schlaegl: > >> To prevent problems with interrupt latency, and due to the fact, that > >> the error will be counted anyway (icount.overrun), the dev_err is simply > >> removed. > >> > >> Background: > >> If an rx-fifo overflow occurs a dev_err message was called in interrupt > >> context. Since dev_err messages are written to console in a synchronous way > >> (unbuffered), and console may be a serial terminal, this leads to a > >> highly increased interrupt-latency (several milliseconds). > >> As a result of the high latency more rx-fifo overflows will happen, and > >> therefore a feedback loop of errors is created. > > > > I understand your rationale but removing this error message from kernel log > > removes the possibility to detect serial overruns by simply check the > > kernel log or output on kernel console. AFAICS you have to use TIOCGICOUNT > > to get the error counters. > > How about introducing a rate limit for this kernel message? > > > > Hello! > > I understand your argument, but: > 1. In my personal opinion kernel error messages should only be used on > internal errors (missing resources, asserts, ...) and in cases where no other > way is (yet) available to report errors (by counters, return values, ...). > Lost RX bytes on uarts seem more like a communication error and should be > silently handled by higher layers using error counters, or protocol internal > mechanisms. > 2. I have found no other serial driver (except serial-tegra and imx) that > reports this kind of errors using kernel messages. > 3. Error counters for serial interfaces can also be retrieved from userspace > by using procfs -> implemented in serial_core; e.g. /proc/tty/driver/IMX-uart.
Ah, I've just noticed those errors will only be written when > 0. I think this is fine. A bit cumbersome for automatic parsing, but reading manually will be ok. Acked-By: Alexander Stein <alexander.st...@systec-electronic.com> Best regards, Alexander Stein -- Dipl.-Inf. Alexander Stein SYS TEC electronic GmbH Am Windrad 2 08468 Heinsdorfergrund Tel.: 03765 38600-1156 Fax: 03765 38600-4100 Email: alexander.st...@systec-electronic.com Website: www.systec-electronic.com Managing Director: Dipl.-Phys. Siegmar Schmidt Commercial registry: Amtsgericht Chemnitz, HRB 28082 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
