I observed higher that usual latencies when running: $ cd /tmp $ taskset 2 stress -d 1 --hdd-bytes 1M & $ timeout 5 taskset 8 cyclictest -p80 -i250 -n -q The maximum latency is 43: T: 0 (3060) P:80 I:250 C: 39980 Min: 6 Act: 15 Avg: 9 Max: 43 When running stress -m, the maximum latency was about 18, which is much smaller than 43. The system is arm64 (Xilinx ZCU102 board) with linux kernel 4.14-rt1. stress -d performs file writes and calls unlink(). I am curious why the maximum latency is more than doubled with stress -d and I wonder if there is any way to improve it. Note that I traced the exectution using ftrace and saw the following call stack: raw_spin_lock_irqsave task_rq_lock migrate_disable_update_cpus_allowed migrate_disable pagefault_disable kmap_atomic iov_iter_copy_from_user_atomic generic_perform_write __generic_file_write_iter __vfs_write I guess that raw_spin_lock_irqsave disables interrupts, but I'm not sure if this is the cause of the high latency. ftrace says that migrate_disable takes about 20 microseconds and migrate_enable another 20 microseconds, but ftrace itself has some overhead.
