On 2021-12-17 09:25:25 [-0800], Song Liu wrote:
The delay is a jiffy so it depends on CONFIG_HZ. You do benchmark for the best algorithm and if you get preempted during that period then your results may be wrong and you make a bad selection.
With current code, the delay _should be_ 16 jiffies. However, the experiment hits way longer latencies. I agree this may cause inaccurate benchmark results and thus suboptimal RAID algorithm.
Everything less than CONFIG_PREEMPT does not have an explicit requirement for preemption so higher latencies are not unusual. *If* this is a problem on <= PREEMPT_VOLUNTARY then a cond_resched() between loops would be the usual thing to do. But only *if* it is a real problem which I doubt. It is not a preemtible kernel after all…
I guess the key question is whether long latency at module loading time matters. If that doesn't matter, we should just drop this.
Correct. And should this be problematic on PREEMPT_RT then I would restrict CONFIG_RAID6_PQ_BENCHMARK to !PREEMPT_RT.
Thanks, Song
Sebastian