On Thu, 20 Feb 2014, Peter Hurley wrote:

On 02/19/2014 09:55 PM, Peter Hurley wrote:

quoted

On 02/19/2014 06:06 PM, Hal Murray wrote:

quoted

quoted

Can you give me an idea of your device's average and minimum required
latency (please be specific)?  Is your target arch x86 [so I can
evaluate the
the impact of bus-locked instructions relative to your expected]?

The code I'm familiar with is ntpd and gpsd.  They run on almost any
hardware
or OS and talk to a wide collection of devices.

There is no hard requirement for latency.  They just work better with
lower
latency.  The lower the better.

People gripe about the latency due to USB polling which is about a ms.

Have you tried 3.12+ without low_latency? I ripped out a lot of locks
from 3.12+ so it's possible it already meets your requirements.

Using Alan's idea to mock up a latency test, I threw together a test jig
using two computers running 3.14-rc1 and my fwserial driver (modified to
not aggregrate writes) in raw mode where the target does this:

This is a complete pointless test. Use a bog standard 8250 UART on the
PC and connect a microcontroller on the other end which serves you an
continous stream of data at 115200 Baud.

There is no way you can keep up with that without the low latency
option neither on old and nor on new machines if you have enough other
stuff going on in the system.

Thanks,

	tglx