Messages in this thread | | | Date | Thu, 26 Sep 2013 12:27:23 -0700 | Subject | Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file | From | Jason Low <> |
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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?
> + return; > + } > + ACCESS_ONCE(prev->next) = node; > + smp_wmb(); > + /* Wait until the lock holder passes the lock down */ > + while (!ACCESS_ONCE(node->locked)) > + arch_mutex_cpu_relax(); > +} > + > +static void mcs_spin_unlock(struct mcs_spin_node **lock, struct mcs_spin_node *node) > +{ > + struct mcs_spin_node *next = ACCESS_ONCE(node->next); > + > + if (likely(!next)) { > + /* > + * Release the lock by setting it to NULL > + */ > + if (cmpxchg(lock, node, NULL) == node)
And can we make this check likely()?
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