On Tue, Oct 08, 2013 at 01:34:55PM -0700, Tim Chen wrote:
> On Tue, 2013-10-08 at 16:51 -0300, Rafael Aquini wrote:
> > On Wed, Oct 02, 2013 at 03:38:32PM -0700, Tim Chen wrote:
> > > We will need the MCS lock code for doing optimistic spinning for rwsem.
> > > Extracting the MCS code from mutex.c and put into its own file allow us
> > > to reuse this code easily for rwsem.
> > >
> > > Reviewed-by: Ingo Molnar <mingo@xxxxxxx>
> > > Reviewed-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
> > > ---
> > > include/linux/mcs_spinlock.h | 64 ++++++++++++++++++++++++++++++++++++++++++
> > > include/linux/mutex.h | 5 ++-
> > > kernel/mutex.c | 60 ++++----------------------------------
> > > 3 files changed, 74 insertions(+), 55 deletions(-)
> > > create mode 100644 include/linux/mcs_spinlock.h
> > >
> > > diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h
> > > new file mode 100644
> > > index 0000000..b5de3b0
> > > --- /dev/null
> > > +++ b/include/linux/mcs_spinlock.h
> > > @@ -0,0 +1,64 @@
> > > +/*
> > > + * MCS lock defines
> > > + *
> > > + * This file contains the main data structure and API definitions of MCS lock.
> > > + *
> > > + * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock
> > > + * with the desirable properties of being fair, and with each cpu trying
> > > + * to acquire the lock spinning on a local variable.
> > > + * It avoids expensive cache bouncings that common test-and-set spin-lock
> > > + * implementations incur.
> > > + */
> >
> > nitpick:
> >
> > I believe you need
> >
> > +#include <asm/processor.h>
> >
> > here, to avoid breaking the build when arch_mutex_cpu_relax() is not defined
> > (arch/s390 is one case)
>
Humm... sorry by my noise as I was looking into an old tree, before this commit:
commit 083986e8248d978b6c961d3da6beb0c921c68220
Author: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Date: Sat Sep 28 11:23:59 2013 +0200
mutex: replace CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX with simple ifdef
> Probably
>
> +#include <linux/mutex.h>
>
Yeah, but I guess right now you're ok without it, as the only place this
header is included is in kernel/mutex.c and it linux/mutex.h get in before us.
If the plan is to extend usage for other places where mutex.h doesn't go, then
perhaps the better thing would be just copycat the same #ifdef here.
Cheers! (and sorry again for the noise)
> should be added instead?
> It defines arch_mutex_cpu_relax when there's no
> architecture specific version.
>
> Thanks.
> Tim
>
>
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