On Thu, Mar 17, 2022 at 11:19 AM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote:
>
> On Wed, Mar 16, 2022 at 03:45:48PM -0700, Namhyung Kim wrote:
> > Adding the lock contention tracepoints in various lock function slow
> > paths. Note that each arch can define spinlock differently, I only
> > added it only to the generic qspinlock for now.
> >
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> > kernel/locking/mutex.c | 3 +++
> > kernel/locking/percpu-rwsem.c | 3 +++
> > kernel/locking/qrwlock.c | 9 +++++++++
> > kernel/locking/qspinlock.c | 5 +++++
> > kernel/locking/rtmutex.c | 11 +++++++++++
> > kernel/locking/rwbase_rt.c | 3 +++
> > kernel/locking/rwsem.c | 9 +++++++++
> > kernel/locking/semaphore.c | 14 +++++++++++++-
> > 8 files changed, 56 insertions(+), 1 deletion(-)
> >
>
> [...]
>
> > diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
> > index 9ee381e4d2a4..e3c19668dfee 100644
> > --- a/kernel/locking/semaphore.c
> > +++ b/kernel/locking/semaphore.c
> > @@ -32,6 +32,7 @@
> > #include <linux/semaphore.h>
> > #include <linux/spinlock.h>
> > #include <linux/ftrace.h>
> > +#include <trace/events/lock.h>
> >
> > static noinline void __down(struct semaphore *sem);
> > static noinline int __down_interruptible(struct semaphore *sem);
> > @@ -209,6 +210,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
> > long timeout)
> > {
> > struct semaphore_waiter waiter;
> > + bool tracing = false;
> >
> > list_add_tail(&waiter.list, &sem->wait_list);
> > waiter.task = current;
> > @@ -220,18 +222,28 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
> > if (unlikely(timeout <= 0))
> > goto timed_out;
> > __set_current_state(state);
> > + if (!tracing) {
> > + trace_contention_begin(sem, 0);
> > + tracing = true;
> > + }
> > raw_spin_unlock_irq(&sem->lock);
> > timeout = schedule_timeout(timeout);
> > raw_spin_lock_irq(&sem->lock);
> > - if (waiter.up)
> > + if (waiter.up) {
> > + trace_contention_end(sem, 0);
> > return 0;
> > + }
> > }
> >
> > timed_out:
> > + if (tracing)
> > + trace_contention_end(sem, -ETIME);
> > list_del(&waiter.list);
> > return -ETIME;
> >
> > interrupted:
> > + if (tracing)
> > + trace_contention_end(sem, -EINTR);
> > list_del(&waiter.list);
> > return -EINTR;
> > }
>
> why not simply remove tracing variable and call trace_contention_begin()
> earlier like in rwsem? we can ignore it if ret != 0.
Right, will change. But we should not ignore the return value.
Thanks,
Namhyung
