> 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. If vm is not overcommit, guest should have KVM_HINTS_REALTIME, I think native qspinlock should be better Could you try test this patch https://patchwork.kernel.org/project/kvm/patch/20250722110005.4988-1-lirongqing@xxxxxxxxx/ Furthermore, I think the virt_spin_lock needs to be optimized. Br -Li > 2. the critical section is very short; spin wait is faster than pv_kick. > > BR > Wangyang
