On Thu, Aug 14, 2025 at 01:26:59AM +0000, Guo, Wangyang wrote: > On 8/13/2025 10:33 PM, Peter Zijlstra wrote: > > On Wed, Aug 13, 2025 at 08:50:43AM +0800, Wangyang Guo wrote: > >> When multiple threads waiting for lock at the same time, once lock owner > >> releases the lock, waiters will see lock available and all try to lock, > >> which may cause an expensive CAS storm. > >> > >> Binary exponential backoff is introduced. As try-lock attempt increases, > >> there is more likely that a larger number threads compete for the same > >> lock, so increase wait time in exponential. > > > > You shouldn't be using virt_spin_lock() to begin with. That means you've > > misconfigured your guest. > > > > We have paravirt spinlocks for a reason. > > We have tried PARAVIRT_SPINLOCKS, it can help to reduce the contention cycles, but the throughput is not good. I think there are two factors: > > 1. the VM is not overcommit, each thread has its CPU resources to doing spin wait. In the non-overcommit, physically pinned case, there is a knob to use native spinlocks.
