lkml.org 
[lkml]   [2020]   [Feb]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[tip: locking/core] locking/percpu-rwsem: Move __this_cpu_inc() into the slowpath
    The following commit has been merged into the locking/core branch of tip:

    Commit-ID: 71365d40232110f7b029befc9033ea311d680611
    Gitweb: https://git.kernel.org/tip/71365d40232110f7b029befc9033ea311d680611
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Wed, 30 Oct 2019 20:17:51 +01:00
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitterDate: Tue, 11 Feb 2020 13:10:54 +01:00

    locking/percpu-rwsem: Move __this_cpu_inc() into the slowpath

    As preparation to rework __percpu_down_read() move the
    __this_cpu_inc() into it.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
    Acked-by: Will Deacon <will@kernel.org>
    Acked-by: Waiman Long <longman@redhat.com>
    Tested-by: Juri Lelli <juri.lelli@redhat.com>
    Link: https://lkml.kernel.org/r/20200131151540.041600199@infradead.org
    ---
    include/linux/percpu-rwsem.h | 10 ++++++----
    kernel/locking/percpu-rwsem.c | 2 ++
    2 files changed, 8 insertions(+), 4 deletions(-)

    diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
    index 4ceaa19..bb5b71c 100644
    --- a/include/linux/percpu-rwsem.h
    +++ b/include/linux/percpu-rwsem.h
    @@ -59,8 +59,9 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
    * and that once the synchronize_rcu() is done, the writer will see
    * anything we did within this RCU-sched read-size critical section.
    */
    - __this_cpu_inc(*sem->read_count);
    - if (unlikely(!rcu_sync_is_idle(&sem->rss)))
    + if (likely(rcu_sync_is_idle(&sem->rss)))
    + __this_cpu_inc(*sem->read_count);
    + else
    __percpu_down_read(sem, false); /* Unconditional memory barrier */
    /*
    * The preempt_enable() prevents the compiler from
    @@ -77,8 +78,9 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
    /*
    * Same as in percpu_down_read().
    */
    - __this_cpu_inc(*sem->read_count);
    - if (unlikely(!rcu_sync_is_idle(&sem->rss)))
    + if (likely(rcu_sync_is_idle(&sem->rss)))
    + __this_cpu_inc(*sem->read_count);
    + else
    ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
    preempt_enable();
    /*
    diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
    index 969389d..becf925 100644
    --- a/kernel/locking/percpu-rwsem.c
    +++ b/kernel/locking/percpu-rwsem.c
    @@ -47,6 +47,8 @@ EXPORT_SYMBOL_GPL(percpu_free_rwsem);

    bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
    {
    + __this_cpu_inc(*sem->read_count);
    +
    /*
    * Due to having preemption disabled the decrement happens on
    * the same CPU as the increment, avoiding the
    \
     
     \ /
      Last update: 2020-02-11 13:50    [W:2.334 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site