linux-kernel - Re: [PATCH 2/2] locking: Apply contention tracepoints in the slow path

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Message-ID: <20220318132833.GB1665646@odroid>
Date:   Fri, 18 Mar 2022 13:28:33 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnd Bergmann <arnd@...db.de>,
        Radoslaw Burny <rburny@...gle.com>, linux-arch@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH 2/2] locking: Apply contention tracepoints in the slow
 path

On Fri, Mar 18, 2022 at 01:24:24PM +0000, Hyeonggon Yoo wrote:
> On Fri, Mar 18, 2022 at 08:55:32PM +0800, Boqun Feng wrote:
> > On Wed, Mar 16, 2022 at 03:45:48PM -0700, Namhyung Kim wrote:
> > [...]
> > > @@ -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);
> > 
> > This looks a littl ugly ;-/
> 
> I agree this can be simplified a bit.
> 
> > Maybe we can rename __down_common() to
> > ___down_common() and implement __down_common() as:
> > 
> > 	static inline int __sched __down_common(...)
> > 	{
> > 		int ret;
> > 		trace_contention_begin(sem, 0);
> > 		ret = ___down_common(...);
> > 		trace_contention_end(sem, ret);
> > 		return ret;
> > 	}
> > 
> > Thoughts?
> >
> 
> But IMO inlining tracepoints is generally not a good idea.
> Will increase kernel size a lot.
>

Ah, it's already inlined. Sorry.

> > Regards,
> > Boqun
> > 
> > > +			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;
> > >  }
> > > -- 
> > > 2.35.1.894.gb6a874cedc-goog
> > >