Hello, On Sat, Jul 5, 2008 at 2:59 PM, <leon.woestenberg@xxxxxxxxx> wrote: > The faulty case was a non-FIFO serial driver that deferred LED blinking to > a workqueue using schedule_work(). However, that work used GPIO bitbanged I2C, > which uses 50 usecs udelay()s. With the work inheriting the serial IRQ priority, > it easily missed the ~60 usec deadline of 115200 bps communications. > John Kacur asked forthe (custom) code showing this case on IRC. I suspect the current kernel also has drivers that *also* depend on workqueue's not pre-empting or delaying their calling interrupt handler. See http://www.sidebranch.com/leon/ for the code. A short file roadmap and explanation of the analysis: lowlevel_16550.c: non-FIFO UART driver axonbus.c: protocol handler max7311.c: I2C -> GPIO extender, driving a few LEDs. Queueing the "blink a LED" work happens in this code path: lowlevel_16550.c:axonbus_isr() -> axonbus.c:ab_cmd_receive() -> boardsupport.c:ll_blink() The queued work then performs this code path, running at the same real-time priority as the originating IRQ: ll_blink_work() -> do_max7311_read() -> i2c-algo-bit.c:* -> udelay(50) The udelay(50) thus keeps the 16550 interrupt from being serviced. Scheduling the work at lower priority solved this. Regards, Leon. p.s. we will submit the max7311 driver for upstream. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
