Messages in this thread |  | | | Date | Thu, 17 Aug 2006 11:40:47 -0500 | | From | Paul Fulghum <> | | Subject | Re: How to avoid serial port buffer overruns? |
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Raphael Hertzog wrote: > I tried 2.6.17.7. > > But I'm really not sure that the 2.6 is a regression from 2.4, in fact I > think it does better by default. > > The stock 2.4.31 kernel I was using had serial overruns at 9600 bauds > already. Once patched with the low latency/preemptive kernel patchs, it > was way better and I had only overruns at 115200 bauds. > > With the 2.6.17.7 kernel (configured with CONFIG_PREEMPT and > CONFIG_HZ=1000), I'm seeing overruns starting at 38400 bauds. So > compared to plain 2.4, it's better. However compared to the patched > 2.4, it's worse.
This tells me your issue is not a problem with the serial or tty code, but rather a matter of IRQ latency. (Which you may have already known, but I was unclear on) I do not expect 2.6.18-rc4 to make a difference.
For fun, have you tried playing with the rx FIFO trigger level in the 16550A entry in drivers/serial/8250.c ? You could try replacing UART_FCR_R_TRIG_10 (8 char trigger) with UART_FCR_R_TRIG_01 (4 char trigger) or even UART_FCR_R_TRIG_00 (1 char trigger). That creates more interrupts, but allows more time to activate the ISR before overrun.
Lee's issue may still merit investigation into the serial/tty code.
-- Paul Fulghum Microgate Systems, Ltd. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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