On Mon, Jun 8, 2015 at 4:15 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Jun 08, 2015 at 03:28:21PM -0400, Steven Walter wrote: >> Ports that are marked low-latency get their own kthread that is >> high-priority. >> >> Signed-off-by: Steven Walter <stevenrwalter@xxxxxxxxx> >> --- >> drivers/tty/tty_buffer.c | 14 +++++++++++++- >> 1 file changed, 13 insertions(+), 1 deletion(-) > > What kind of measurements have you done to show that these changes > actually matter? The application that benefits from this is driving a motor controller card over an RS-232 link. The userspace application that communicates over the TTY needs to respond to received bytes within about 1ms. Without this patch, I have observed (via ftrace) the kworker threads get delayed by over 100ms, meaning the real-time thread of the userspace application isn't even woken up until 100ms after the byte is received. With this patch, I have not observed a single instance of communications failure (i.e., we reliably meet our real-time deadline). Hope that helps -- -Steven Walter <stevenrwalter@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
