On 24.06.22 17:01, Stephen Hemminger wrote:
On Thu, 23 Jun 2022 21:03:49 +0200 Carsten Andrich <carsten.andr...@tu-ilmenau.de> wrote:2. Use real-time priority (SCHED_FIFO w/ priority 99) for the DPDK threads and echo -1 > /proc/sys/kernel/sched_rt_runtime_us to disable the runtime limit. With the runtime limit in place, the SCHED_FIFO performance will be significantly worse than SCHED_OTHER.This can cause major issues if application is normal DPDK application (never does system calls). If an interrupt or other event happens on your isolated CPU, the work that it would do in soft irq is never performed. FIFO has higher priority than kernel threads. This can lead to mystery lockups from other applications (reads not completing, network timeouts, etc).
Thanks for pointing that out. Do you know of any official kernel documentation that could shed some light on that? I haven't had any serious issues like the ones you list, but maybe I've been lucky. My DPDK applications typically run on fairly minimal systems used exclusively for DPDK tasks, which require minimal latency/jitter. Minor side-effects from using SCHED_FIFO are tolerable in my case, if it improves performance.
In any semi-recent kernel using SCHED_NO_HZ_FULL will keep clock ticks from happening on the isolated cores.
On 24.06.22 18:42, Stephen Hemminger wrote:
Sorry, wrong option. Full docs here: https://docs.kernel.org/timers/no_hz.html
Thanks. nohz_full is already in the list of kernel cmdline options I use. Best regards, Carsten
