On 14.04.25 17:05, Sebastian Andrzej Siewior wrote: > On 2025-04-14 20:20:04 [+0530], K Prateek Nayak wrote: >> Note: I could not reproduce the splat with !PREEMPT_RT kernel >> (CONFIG_PREEMPT=y) or with small loops counts that don't exhaust the >> cfs bandwidth. > > Not sure what this has to do with anything. > On !RT the read_lock() in the timer can be acquired even with a pending > writer. The writer keeps spinning until the main thread is gone. There > should be no RCU boosting but the RCU still is there, too. > > On RT the read_lock() in the timer block, the write blocks, too. So > every blocker on the lock is scheduled out until the reader is gone. On > top of that, the reader gets RCU boosted with FIFO-1 by default to get > out. There is no boosting of the active readers on RT as there is no information recorded about who is currently holding a read lock. This is the whole point why rwlocks are hairy with RT, I thought. Jan -- Siemens AG, Foundational Technologies Linux Expert Center
