Hi This might well be my basic misunderstanding, or the test was wrong, but the probability is pretty low, so, asking here.
I thought, if a task sleeps on, say, read() and then data come and there's no other runnable task with a higher priority, the sleeping task should be woken up immediately. My test showed that the task is only woken up on the next jiffie. Kernel 2.6.11.10. Details: a program does a cfmakeraw() on a ttyS, and does blocking reads of 1 byte in a loop, taking timestamps with gettimeofday() after waking up. The FIFO is switched off by configuring the UART as 16550. With a low (e.g., 600 baud) baudrate I see indeed that the task gets individual bytes as they arrive. However, if I set the baudrate to, say, 19200 the task is woken up every millisecond (ix86) and then it gets 2 bytes. Another program, opening 2 pipes, forking, and then playing ping-pong between the 2 tasks confirms, that in this case the tasks currently sleeping on read() is woken up immediately as the other one does a write... Test program sources available on request. Is it a conscious decision or is my test wrong? Thanks Guennadi --------------------------------- Guennadi Liakhovetski, Ph.D. DSA Daten- und Systemtechnik GmbH Pascalstr. 28 D-52076 Aachen Germany - 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/
