On 1/7/25 8:59 AM, Kumar Kartikeya Dwivedi wrote:
We ripped out PV and virtualization related bits from rqspinlock in an earlier commit, however, a fair lock performs poorly within a virtual machine when the lock holder is preempted. As such, retain the virt_spin_lock fallback to test and set lock, but with timeout and deadlock detection. We don't integrate support for CONFIG_PARAVIRT_SPINLOCKS yet, as that requires more involved algorithmic changes and introduces more complexity. It can be done when the need arises in the future.
virt_spin_lock() doesn't scale well. It is for hypervisors that don't support PV qspinlock yet. Now rqspinlock() will be in this category.
I wonder if we should provide an option to disable rqspinlock and fall back to the regular qspinlock with strict BPF locking semantics.
Another question that I have is about PREEMPT_RT kernel which cannot tolerate any locking stall. That will probably require disabling rqspinlock if CONFIG_PREEMPT_RT is enabled.
Cheers, Longman
