On Thu, Oct 25, 2007 at 12:44:31PM -0700, Tim Bird wrote: > I've been looking at 'IRQ off' latency in the Linux kernel, on > version 2.6.22 for target using an ARM processor. > I use a serial console, at 115200 bps.
Printk to the serial console uses polled I/O to get deterministic, reliable, and -timely- output. If our very next statement (or interrupt) may lock up the box, we want to be sure our printk has actually been delivered before that happens. Kindof a bummer for realtime, but also rather hard to get around. > I've noticed that calls to printk disable interrupts for > excessively long times. I have a long test printk of > over 200 chars, that holds interrupts off for 24 milliseconds. 2000bits @ 115200bps -> 17.4ms > Are these are really needed, with all this other locking > going on? Any ideas for fixing this? Well, we could have a commandline option that made messages with a priority below X go out buffered. But it'd be a lousy default from a debugging perspective. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
