Messages in this thread | | | Date | Thu, 17 Aug 2006 18:10:42 +0200 | From | Raphael Hertzog <> | Subject | Re: How to avoid serial port buffer overruns? |
| |
On Wed, 16 Aug 2006, Paul Fulghum wrote: > On Wed, 2006-08-16 at 17:12 -0400, Lee Revell wrote: > > 2.6.15 and 2.6.16. Here is the .config: > > Alan's rework of the receive tty buffering went > into 2.6.16 and cured some problems, but clearly not yours. > Some more adjustments are in 2.6.18-rc4, so that > would be interesting to try for diagnosing this.
I will try 2.6.18-rc4 and keep you informed.
> I was wondering if the problem was interrupt latency, > the tty receive buffering, or something totally different. > I don't know if your problem and Raphael's are caused > by the same mechanism. I would still like to know which > kernel versions he has tried.
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.
(the figures are *very approximative* as the overruns haven't been detected with the same test conditions on 2.4 and on 2.6)
I have no result with the 2.6.17.7 patched with the real time patch of Ingo/Thomas since it currently doesn't work on my card (see my separate bugreport).
(those questions may have been directed to Lee but I'll respond in my case as well) > Are you using the low_latency flag on the serial device?
I tried that option with the 2.4 kernel and it didn't improve the situation at all, and I haven't retried it with the 2.6 yet. But I will do.
> What type of UART has been tested (16550? other?)
I'm using only 16550 and I have no choice here, it's an "off the shelf" card.
> Are you seeing overruns or just lost data?
I'm seeing overruns.
Regards, -- Raphaël Hertzog
Premier livre français sur Debian GNU/Linux : http://www.ouaza.com/livre/admin-debian/ - 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/
| |