On 2019-03-24 04:12:33 [+0000], Andy Ng wrote: > Hello there. Hi, > I am using 4.9.11 with rt9 on ARM imx6 soc. I am writing a device > driver and I noticed that my first run of my driver gives big latency > - in the region on 10msec. When I get a gpio interrupt, I schedule > some work and the user waiting on a read() takes reply in about > 10,30msec, on the second run it gets latency down to 140usec. I > changed the tick from 100Hz to 300Hz and 500Hz, I noticed that my > starting latency was dropped to 3400usec and 2320usec respectively. > Which indicate some delays to kickoff for first time the scheduled > work related to the granularity of the timer tick. > Any ideas of what may be wrong? tracing (scheduler) between interrupt and user task should reveal why it takes so long. It might first fork of a worker, there might be other worker busy. Is this delay only limited to RT or is also on !RT? > Thanks > Andy Sebastian
