The numbers you quoted are in the 3 to 30 microsecond range (3,000 to 30,000 nanoseconds). That is too short a time to be a context switch to another thread/process, let the other thread run, and context switch back to your thread. Most likely the core where your process was running was used by the kernel to service an external interrupt (e.g. network card, disk, timer), then returned to running your process.
You can watch the linux interrupt counters (per CPU core and per source) with this command
watch -d -n 0.2 cat /proc/interrupts
The -n 0.2
will cause the command to be issued at 5Hz, the -d
flag will highlight what has changed.
The source of the interrupt could also be a TLB shootdown
, which results in an IPI
(Inter-Processor Interrupt). You can read more about TLB shootdowns here.
If you want to reduce the number of interrupts serviced by the core running your thread/process, you need to set the interrupt affinity. You can learn more about Red Hat Interrupts and IRQ (Interrupt requests) tuning here, and here.
Worth noting is that you are using CLOCK_REALTIME
which isn't guaranteed to be "smooth", it could jump around as the system clock is "disciplined" to keep accurate time by a service like NTP (Network Time Protocol) or PTP (Precision Time Protocol). For your purposes it is better to use CLOCK_MONOTONIC
, you can read more about the difference here. When a clock is "disciplined" the clock can jump by a "step" - this is unusual and certainly not the cause of the many spikes you see.