Re: locking changes in tty broke low latency feature

On 02/20/2014 02:33 PM, Grant Edwards wrote:

On 2014-02-20, Peter Hurley [off-list ref] wrote:

quoted

Sender completes 2000 loops in 160ms total run time;
that's 80us average per complete round-trip.

If I understand correctly, that 80us _includes_ the actual time for
the bits on the wire (which means the actual "baud rate" involved is
high enough that it's negligible).

Yes, 80us includes the transmit time.

quoted

I think this shows that low_latency is unnecessary and should
just be removed/ignored by the tty core.

If that's the sort of latency that you get for typical kernel
configurations for typical distros, then I agree that the low_latency
flag is not needed by the tty later.

Stock ubuntu kernel config but preempt and 250hz (and debugging stuff).

However, it might still be useful for the lower-level tty or
serial-core driver to control CPU usage vs. latency trade-offs (for
exaple, one of my drivers uses it to decide where to set the rx FIFO
threshold).

Sure, it could be left for driver consumption.

Regards,
Peter Hurley