On Wed, Jun 29, 2022 at 2:13 AM Waiman Long <longman@xxxxxxxxxx> wrote: > > On 6/28/22 04:17, guoren@xxxxxxxxxx wrote: > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > > Some architecture has a flexible requirement on the type of spinlock. > > Some LL/SC architectures of ISA don't force micro-arch to give a strong > > forward guarantee. Thus different kinds of memory model micro-arch would > > come out in one ISA. The ticket lock is suitable for exclusive monitor > > designed LL/SC micro-arch with limited cores and "!NUMA". The > > queue-spinlock could deal with NUMA/large-scale scenarios with a strong > > forward guarantee designed LL/SC micro-arch. > > > > So, make the spinlock a combo with feature. > > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> > > Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > > Cc: Arnd Bergmann <arnd@xxxxxxxx> > > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx> > > --- > > include/asm-generic/spinlock.h | 43 ++++++++++++++++++++++++++++++++-- > > kernel/locking/qspinlock.c | 2 ++ > > 2 files changed, 43 insertions(+), 2 deletions(-) > > > > diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h > > index f41dc7c2b900..a9b43089bf99 100644 > > --- a/include/asm-generic/spinlock.h > > +++ b/include/asm-generic/spinlock.h > > @@ -28,34 +28,73 @@ > > #define __ASM_GENERIC_SPINLOCK_H > > > > #include <asm-generic/ticket_spinlock.h> > > +#ifdef CONFIG_ARCH_USE_QUEUED_SPINLOCKS > > +#include <linux/jump_label.h> > > +#include <asm-generic/qspinlock.h> > > + > > +DECLARE_STATIC_KEY_TRUE(use_qspinlock_key); > > +#endif > > + > > +#undef arch_spin_is_locked > > +#undef arch_spin_is_contended > > +#undef arch_spin_value_unlocked > > +#undef arch_spin_lock > > +#undef arch_spin_trylock > > +#undef arch_spin_unlock > > > > static __always_inline void arch_spin_lock(arch_spinlock_t *lock) > > { > > - ticket_spin_lock(lock); > > +#ifdef CONFIG_ARCH_USE_QUEUED_SPINLOCKS > > + if (static_branch_likely(&use_qspinlock_key)) > > + queued_spin_lock(lock); > > + else > > +#endif > > + ticket_spin_lock(lock); > > } > > Why do you use a static key to control whether to use qspinlock or > ticket lock? In the next patch, you have > > +#if !defined(CONFIG_NUMA) && defined(CONFIG_QUEUED_SPINLOCKS) > + static_branch_disable(&use_qspinlock_key); > +#endif > > So the current config setting determines if qspinlock will be used, not > some boot time parameter that user needs to specify. This patch will > just add useless code to lock/unlock sites. I don't see any benefit of > doing that. This is a startup patch for riscv. next, we could let vendors make choices. I'm not sure they like cmdline or vendor-specific errata style. Eventually, we would let one riscv Image support all machines, some use ticket-lock, and some use qspinlock. > > Cheers, > Longman > -- Best Regards Guo Ren ML: https://lore.kernel.org/linux-csky/