Messages in this thread | | | Subject | Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file | From | Davidlohr Bueso <> | Date | Thu, 26 Sep 2013 13:06:47 -0700 |
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On Thu, 2013-09-26 at 12:27 -0700, Jason Low wrote: > On Wed, Sep 25, 2013 at 3:10 PM, Tim Chen <tim.c.chen@linux.intel.com> 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. > > > > Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> > > Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> > > --- > > include/linux/mcslock.h | 58 +++++++++++++++++++++++++++++++++++++++++++++++ > > kernel/mutex.c | 58 +++++----------------------------------------- > > 2 files changed, 65 insertions(+), 51 deletions(-) > > create mode 100644 include/linux/mcslock.h > > > > diff --git a/include/linux/mcslock.h b/include/linux/mcslock.h > > new file mode 100644 > > index 0000000..20fd3f0 > > --- /dev/null > > +++ b/include/linux/mcslock.h > > @@ -0,0 +1,58 @@ > > +/* > > + * MCS lock defines > > + * > > + * This file contains the main data structure and API definitions of MCS lock. > > + */ > > +#ifndef __LINUX_MCSLOCK_H > > +#define __LINUX_MCSLOCK_H > > + > > +struct mcs_spin_node { > > + struct mcs_spin_node *next; > > + int locked; /* 1 if lock acquired */ > > +}; > > + > > +/* > > + * We don't inline mcs_spin_lock() so that perf can correctly account for the > > + * time spent in this lock function. > > + */ > > +static noinline > > +void mcs_spin_lock(struct mcs_spin_node **lock, struct mcs_spin_node *node) > > +{ > > + struct mcs_spin_node *prev; > > + > > + /* Init node */ > > + node->locked = 0; > > + node->next = NULL; > > + > > + prev = xchg(lock, node); > > + if (likely(prev == NULL)) { > > + /* Lock acquired */ > > + node->locked = 1; > > If we don't spin on the local node, is it necessary to set this variable?
I don't follow, the whole idea is to spin on the local variable.
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