On 05/31, Joel Fernandes wrote: > > The problem with traditional read-write semaphores is that when multiple > cores take the lock for reading, the cache line containing the semaphore > is bouncing between L1 caches of the cores, causing performance > degradation. > > However, it appears to me that the struct percpu_rwsem "rss" element > which is used by the RCU-sync is not a per-cpu element. So even in the > fastpath case (only readers and no writers), the cacheline containing > rss is shared and will bounce by multiple CPUs. For that matter, even > the cacheline containing the percpu_rw_semaphore itself will be bounce > among multiple reader CPUs. The readers won't modify this memory? read_lock/unlock will only update the per-cpu counter, ->read_count. Oleg.
