Messages in this thread | | | From | Joel Fernandes <> | Date | Tue, 7 Mar 2023 15:19:23 -0500 | Subject | Re: [PATCH] pstore: Revert pmsg_lock back to a normal mutex |
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On Tue, Mar 7, 2023 at 9:09 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Fri, Mar 03, 2023 at 06:11:34PM +0000, Joel Fernandes wrote: > > What makes the rtmutex spin logic different from normal mutex in this > > scenario, so that rtmutex wants to do that but normal ones dont? > > Regular mutex uses osq 'lock' to serialize waiters and only the top > spinner gets to spin on the mutex itself, this greatly reduces the > contention on the mutex. > > OSQ is FIFO, which is not what RT-mutex needs.
Got it, so basically OSQ ensures fairness as its FIFO and also reduces lock contention because I am guessing the OSQ-spinners are spinning on a per-spinner MCS node (that per-CPU optimistic_spin_node it appears).
This makes perfect sense now, thank you Peter!!!
- Joel
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