Racing against the clock -- hitting a tiny kernel race window

TL;DR:

How to make a tiny kernel race window really large even on kernels without CONFIG_PREEMPT:

• use a cache miss to widen the race window a little bit
• make a timerfd expire in that window (which will run in an interrupt handler - in other words, in hardirq context)
• make sure that the wakeup triggered by the timerfd has to churn through 50000 waitqueue items created by epoll

Racing one thread against a timer also avoids accumulating timing variations from …

kernel tiny