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    Subject[PATCH 02/18] drbd: only wakeup if something changed in update_peer_seq
    Date
    From: Lars Ellenberg <lars.ellenberg@linbit.com>

    This commit got it wrong:
    drbd: Make the peer_seq updating code more obvious

    Make it more clear that update_peer_seq() is supposed to wake up the
    seq_wait queue whenever the sequence number changes.

    We don't need to wake up everytime we receive a sequence number
    that is _different_ from our currently stored "newest" sequence number,
    but only if we receive a sequence number _newer_ than what we already
    have, when we actually change mdev->peer_seq.

    Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
    Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
    ---
    drivers/block/drbd/drbd_receiver.c | 9 +++++----
    1 files changed, 5 insertions(+), 4 deletions(-)

    diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
    index 620f27f..64f658b 100644
    --- a/drivers/block/drbd/drbd_receiver.c
    +++ b/drivers/block/drbd/drbd_receiver.c
    @@ -1737,14 +1737,15 @@ static bool need_peer_seq(struct drbd_conf *mdev)

    static void update_peer_seq(struct drbd_conf *mdev, unsigned int peer_seq)
    {
    - unsigned int old_peer_seq;
    + unsigned int newest_peer_seq;

    if (need_peer_seq(mdev)) {
    spin_lock(&mdev->peer_seq_lock);
    - old_peer_seq = mdev->peer_seq;
    - mdev->peer_seq = seq_max(mdev->peer_seq, peer_seq);
    + newest_peer_seq = seq_max(mdev->peer_seq, peer_seq);
    + mdev->peer_seq = newest_peer_seq;
    spin_unlock(&mdev->peer_seq_lock);
    - if (old_peer_seq != peer_seq)
    + /* wake up only if we actually changed mdev->peer_seq */
    + if (peer_seq == newest_peer_seq)
    wake_up(&mdev->seq_wait);
    }
    }
    --
    1.7.4.1


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