Re: [PATCH v1 3/3] drivers/tty: increase priority for tty_buffer_worker

[Oleksij Rempel]

On 10.01.19 17:30, Greg Kroah-Hartman wrote:
> On Thu, Jan 10, 2019 at 04:19:53PM +0100, Oleksij Rempel wrote:
> > > My gut feel is that if somebody still cares deeply about serial line
> > > latency, they should look at trying to see if they can do some of the
> > > work directly without the bounce to the workqueue. We use workqueues
> > > for a reason, but it's possible that some of it could be avoided at
> > > least in special cases... And yours sounds like a special case.
> >
> > It is for industrial low latency RS-422 based application. The loopback
> > test is just easy way to test/reproduce it without additional hardware.
> >
> > What is good, mainlineable way to implement it?
>
> What is the real problem your systems are having?  Are they serial-port
> limited?  Is latency a big issue?  Trying to tune for a fake workload
> isn't the best way to solve anything :)

The system in question is a high power laser cutter with live image-based inspection
and adjustment of the cutting process. In this setup the RS422 interface is used to
control parameters of the laser cutting unit in a tie control loop with the camera.
This loops needs to operate at 1000 Hz.

The xy-stage moves with a speed of approx. 60m/min, i.e. within 1ms it
moves about 1mm. For a high precision control process a jitter of  500 us (+/- 0.5mm)
is unacceptable.

Kind regards,
Oleksij Rempel

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