linux-kernel - Re: [PATCH -tip/master 3/7] locking/mcs: Remove obsolete comment

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Date:	Mon, 28 Jul 2014 10:49:35 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Davidlohr Bueso <davidlohr@...com>, mingo@...nel.org, aswin@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip/master 3/7] locking/mcs: Remove obsolete comment

On Mon, 2014-07-28 at 18:54 +0200, Peter Zijlstra wrote:
> On Mon, Jul 28, 2014 at 09:49:35AM -0700, Jason Low wrote:
> > On Sun, 2014-07-27 at 22:18 -0700, Davidlohr Bueso wrote:
> > > ... as we clearly inline mcs_spin_lock() now.
> > > 
> > > Signed-off-by: Davidlohr Bueso <davidlohr@...com>
> > > ---
> > >  kernel/locking/mcs_spinlock.h | 3 ---
> > >  1 file changed, 3 deletions(-)
> > > 
> > > diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
> > > index 23e89c5..4d60986 100644
> > > --- a/kernel/locking/mcs_spinlock.h
> > > +++ b/kernel/locking/mcs_spinlock.h
> > > @@ -56,9 +56,6 @@ do {									\
> > >   * If the lock has already been acquired, then this will proceed to spin
> > >   * on this node->locked until the previous lock holder sets the node->locked
> > >   * in mcs_spin_unlock().
> > > - *
> > > - * We don't inline mcs_spin_lock() so that perf can correctly account for the
> > > - * time spent in this lock function.
> > >   */
> > >  static inline
> > >  void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
> > 
> > Likewise, I'm wondering if we should make this function noinline so that
> > "perf can correctly account for the time spent in this lock function".
> 
> What's that about anyhow?

So if the function is inlined, perf report would show the contention
occurring in the calling function rather than the inlined function. As
an example, if we were to convert osq_lock() and mutex_spin_on_owner()
to inline, perf would report all the contention from both of those
functions occurring in just "__mutex_lock_slowpath()".


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