On Tue, Sep 22, 2026 at 03:09:46PM +0800, Kunwu Chan wrote: > Hi all, >
Hello Kunwu, > This RFC/WIP extends the current v3 hazptr implementation [1] and > adapts the lockdep use case from Boqun Feng's earlier hazptr series [2] > to the current hazptr API. > > [1] https://lore.kernel.org/all/[email protected]/ > [2] https://lore.kernel.org/lkml/[email protected]/ > > The lockdep conversion replaces the expedited RCU wait in > lockdep_unregister_key() with hazptr_synchronize() for dynamic-key > lookups. > > The series also adds a shared-scan kthread for concurrent > hazptr_synchronize() callers, rcuscale support, and an LKMM test > for the acquire-before-scan ordering. > Thanks a lot for picking up this, much appreciated. Do you happen to play a bit with rcuscale and see any performance difference between hazptr_synchronize() vs synchronize_{s}rcu() on various configs? > I tested the lockdep path on a 96-CPU ARM64 KVM guest with Boqun's > original mq workload [2]. With a multiqueue virtio-net device > (`-device virtio-net-pci,mq=on,vectors=6`), tc mq add/del x100 > completed in 850 ms with hazptr and 860 ms with expedited RCU. > The rmmod workload similarly showed no measurable difference > (1360 ms vs. 1380 ms over 10 runs). There were no crashes or hangs > in these tests. > You could also use /proc/interrupts to measure the IPI counts during the whole operation, and you should be able to see the difference there. Regards, Boqun > This is still RFC/WIP. I would appreciate feedback on the shared-scan > design and the lockdep conversion. > > Kunwu Chan (4): > hazptr: add shared-scan kthread > locking/lockdep: use hazptr to wait for dynamic key lookups > rcuscale: add hazptr scale type > Documentation/litmus-tests: add hazptr acquire-before-scan test > > .../hazptr/hazptr-acquire-before-scan.litmus | 49 ++++ > kernel/hazptr.c | 274 ++++++++++++++++++ > kernel/locking/lockdep.c | 30 +- > kernel/rcu/rcuscale.c | 65 ++++- > 4 files changed, 407 insertions(+), 11 deletions(-) > create mode 100644 > Documentation/litmus-tests/hazptr/hazptr-acquire-before-scan.litmus > > -- > 2.43.0 >
