jignesh patel

CPU interrupts affinity on IMX6Q

Discussion created by jignesh patel on Aug 5, 2018

Hi All,

 

Processor : IMX6Q (MCIMX6Q6AVT10AD)

Linux Kernel : 4.9.11

Kernel reference : wandboard_imx_4.9.11_1.0.0_ga

 

  • We are making IMX6Q based product. In our product we use USB modems for data transmission.
  • In IMX6Q there are 4 Cortex-A9 cores. What we observe is mostly all the interrupts are coming on CPU0 core.
  • Theoretically it should equally distribute to all the cores.
  • I search and read about interrupt affinity.  LXR / The Linux Cross Reference and tried change affinity mask (smp_affinity) for the process which is responsible for data transmission.
  • But what I observe is event though I changed mask (smp_affinity) it not distributed to all the cores it always fall on any CPU at a time.
  • Default affinity mask (smp_affinity) value is "0xF" which is correct to distribute interrupts on all the four cores but behavior is different.
  • Question is why this mask has no effect? Am I missing anything?
  • Second observation is not all the process are have smp_affinity mask. May I know what is reason behind it?

Any suggestion/direction/comment would be appreciated.

 

Thanks,

Jignesh

Outcomes