Re: [PATCH 0/2] net: davinci_cpdma: reduce latency on -rt

On Tue, Jul 26, 2016 at 05:36:49PM +0300, Grygorii Strashko wrote:

On 07/26/2016 03:02 PM, Uwe Kleine-König wrote:

quoted

Hello,

these patches are based on next-20160726. I didn't check yet how latency
improves by using these patches, but even if the improvment is small,
it's still a good idea to have them.

Sry, but how this will affect on -RT? This is not a raw locks, so
they will be converted to rt-mutexes which are sleepable.
Or I've missed smth?

They are still locks after all. On -rt I saw for the relevant
application:

  send package         |
    take lock          |
    write pckt to hw   |
                       | rcv irq
		       |   take lock
		       |     schedule
    drop lock	       | 
      schedule         |
                       |   get pckt from hw
		       |   drop lock

So reducing the time a lock is taken reduces the chances that the lock
is contended for another thread which results in extra context switches.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |