On Thu, Apr 16, 2026 at 03:05:11PM +0000, Dmitry Ilvokhin wrote: > Use the arch-overridable queued_spin_release(), introduced in the > previous commit, to ensure the tracepoint works correctly across all > architectures, including those with custom unlock implementations (e.g. > x86 paravirt). > > When the tracepoint is disabled, the only addition to the hot path is a > single NOP instruction (the static branch). When enabled, the contention > check, trace call, and unlock are combined in an out-of-line function to > minimize hot path impact, avoiding the compiler needing to preserve the > lock pointer in a callee-saved register across the trace call. > > Binary size impact (x86_64, defconfig): > uninlined unlock (common case): +680 bytes (+0.00%) > inlined unlock (worst case): +83659 bytes (+0.21%) > > The inlined unlock case could not be achieved through Kconfig options on > x86_64 as PREEMPT_BUILD unconditionally selects UNINLINE_SPIN_UNLOCK on > x86_64. The UNINLINE_SPIN_UNLOCK guards were manually inverted to force > inline the unlock path and estimate the worst case binary size increase. > > In practice, configurations with UNINLINE_SPIN_UNLOCK=n have already > opted against binary size optimization, so the inlined worst case is > unlikely to be a concern. > > Architectures with fully custom qspinlock implementations (e.g. > PowerPC) are not covered by this change. > > Signed-off-by: Dmitry Ilvokhin <[email protected]>
Much nicer split out! Acked-by: Paul E. McKenney <[email protected]> > --- > include/asm-generic/qspinlock.h | 18 ++++++++++++++++++ > kernel/locking/qspinlock.c | 8 ++++++++ > 2 files changed, 26 insertions(+) > > diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h > index df76f34645a0..915a4c2777f6 100644 > --- a/include/asm-generic/qspinlock.h > +++ b/include/asm-generic/qspinlock.h > @@ -41,6 +41,7 @@ > > #include <asm-generic/qspinlock_types.h> > #include <linux/atomic.h> > +#include <linux/tracepoint-defs.h> > > #ifndef queued_spin_is_locked > /** > @@ -129,12 +130,29 @@ static __always_inline void queued_spin_release(struct > qspinlock *lock) > } > #endif > > +DECLARE_TRACEPOINT(contended_release); > + > +extern void queued_spin_release_traced(struct qspinlock *lock); > + > /** > * queued_spin_unlock - unlock a queued spinlock > * @lock : Pointer to queued spinlock structure > + * > + * Generic tracing wrapper around the arch-overridable > + * queued_spin_release(). > */ > static __always_inline void queued_spin_unlock(struct qspinlock *lock) > { > + /* > + * Trace and release are combined in queued_spin_release_traced() so > + * the compiler does not need to preserve the lock pointer across the > + * function call, avoiding callee-saved register save/restore on the > + * hot path. > + */ > + if (tracepoint_enabled(contended_release)) { > + queued_spin_release_traced(lock); > + return; > + } > queued_spin_release(lock); > } > > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index af8d122bb649..c72610980ec7 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -104,6 +104,14 @@ static __always_inline u32 > __pv_wait_head_or_lock(struct qspinlock *lock, > #define queued_spin_lock_slowpath native_queued_spin_lock_slowpath > #endif > > +void __lockfunc queued_spin_release_traced(struct qspinlock *lock) > +{ > + if (queued_spin_is_contended(lock)) > + trace_contended_release(lock); > + queued_spin_release(lock); > +} > +EXPORT_SYMBOL(queued_spin_release_traced); > + > #endif /* _GEN_PV_LOCK_SLOWPATH */ > > /** > -- > 2.52.0 >
