Hello, i think I noticed a priority inversion regarding workqueues. I have a high- prio task (SCHED_FIFO prio 69) that reads a file in sysfs which actually starts a SPI transfer (4 Bytes). I already boosted (manually) the IRQ thread to SCHED_FIFO prio 96 and also the workqueue (imx35-cspi.0) attached to the SPI driver (spi-imx). The execution time of my task is usually about 600us, but with that SPI it sometimes (well rather often though) it is of about 2ms or even mugh higher. When I remove the SPI transfer from the driver behing the sysfs file the execution time is rather stable, so the problem lies in that SPI transfer. After trying some debug output I came to the conclusion i have change the priority of [kworker/u:1] to SCHED_FIFO prio 97 in my case. I think this should be done automatically. To be held: I do not know what [kworker/u:1] actually is. There seem to be a task for that workqueue already, so what is this kworker? BTW: This is a v3.4.33-rt47 kernel. As the some low priority tasks can delay my high-prio task waiting for SPI transfer completion this seems like priority inversion to me. Any opinions? Best regards, Alexander PS: I tried a 3.10.39-rt40 kernel and the problem is still the same, just the kworker task names have changed. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
