Re: [PATCH] powerpc/qspinlock: Add spinlock contention tracepoint

[Christophe Leroy]

Le 25/07/2025 à 10:14, Nysal Jan K.A. a écrit :
Add a lock contention tracepoint in the queued spinlock slowpath.
Also add the __lockfunc annotation so that in_lock_functions()
works as expected.

Signed-off-by: Nysal Jan K.A. <ny...@linux.ibm.com>
---
  arch/powerpc/lib/qspinlock.c | 13 ++++++++-----
  1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
index bcc7e4dff8c3..622e7f45c2ce 100644
--- a/arch/powerpc/lib/qspinlock.c
+++ b/arch/powerpc/lib/qspinlock.c
@@ -9,6 +9,7 @@
  #include <linux/sched/clock.h>
  #include <asm/qspinlock.h>
  #include <asm/paravirt.h>
+#include <trace/events/lock.h>
  
  #define MAX_NODES	4
  
@@ -708,8 +709,9 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
        qnodesp->count--;
  }
  
-void queued_spin_lock_slowpath(struct qspinlock *lock)
+void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock)
  {
+       trace_contention_begin(lock, LCB_F_SPIN);
        /*
         * This looks funny, but it induces the compiler to inline both
         * sides of the branch rather than share code as when the condition
@@ -718,16 +720,17 @@ void queued_spin_lock_slowpath(struct qspinlock *lock)
        if (IS_ENABLED(CONFIG_PARAVIRT_SPINLOCKS) && is_shared_processor()) {
                if (try_to_steal_lock(lock, true)) {
                        spec_barrier();
-                       return;
+               } else {
+                       queued_spin_lock_mcs_queue(lock, true);

If I read correctly, now all this is single line so you have to drop the 
braces , see 
https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces

                }
-               queued_spin_lock_mcs_queue(lock, true);
        } else {
                if (try_to_steal_lock(lock, false)) {
                        spec_barrier();
-                       return;
+               } else {
+                       queued_spin_lock_mcs_queue(lock, false);
                }

Same here.

-               queued_spin_lock_mcs_queue(lock, false);
        }
+       trace_contention_end(lock, 0);
  }
  EXPORT_SYMBOL(queued_spin_lock_slowpath);