netdev - Re: [PATCH][net-next] openvswitch: change the data type of error status to atomic_long

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Message-ID: <CALnjE+o121kh+hEtEsSLJqBw68dy=epEsXGVDN5wv+4g1xph+g@mail.gmail.com>
Date:	Sat, 6 Sep 2014 20:44:04 -0700
From:	Pravin Shelar <pshelar@...ira.com>
To:	roy.qing.li@...il.com
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH][net-next] openvswitch: change the data type of error
 status to atomic_long_t

On Sat, Sep 6, 2014 at 4:06 AM,  <roy.qing.li@...il.com> wrote:
> From: Li RongQing <roy.qing.li@...il.com>
>
> Change the date type of error status from u64 to atomic_long_t, and use atomic
> operation, then remove the lock which is used to protect the error status.
>
> The operation of atomic maybe faster than spin lock.

What is reason for this change?

>
> Cc: Pravin Shelar <pshelar@...ira.com>
> Signed-off-by: Li RongQing <roy.qing.li@...il.com>
> ---
>  net/openvswitch/vport.c |   25 ++++++++-----------------
>  net/openvswitch/vport.h |   10 ++++------
>  2 files changed, 12 insertions(+), 23 deletions(-)
>
> diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
> index 6d8f2ec..f7e63f9 100644
> --- a/net/openvswitch/vport.c
> +++ b/net/openvswitch/vport.c
> @@ -148,8 +148,6 @@ struct vport *ovs_vport_alloc(int priv_size, const struct vport_ops *ops,
>                 return ERR_PTR(-ENOMEM);
>         }
>
> -       spin_lock_init(&vport->stats_lock);
> -
>         return vport;
>  }
>
> @@ -268,14 +266,10 @@ void ovs_vport_get_stats(struct vport *vport, struct ovs_vport_stats *stats)
>          * netdev-stats can be directly read over netlink-ioctl.
>          */
>
> -       spin_lock_bh(&vport->stats_lock);
> -
> -       stats->rx_errors        = vport->err_stats.rx_errors;
> -       stats->tx_errors        = vport->err_stats.tx_errors;
> -       stats->tx_dropped       = vport->err_stats.tx_dropped;
> -       stats->rx_dropped       = vport->err_stats.rx_dropped;
> -
> -       spin_unlock_bh(&vport->stats_lock);
> +       stats->rx_errors  = atomic_long_read(&vport->err_stats.rx_errors);
> +       stats->tx_errors  = atomic_long_read(&vport->err_stats.tx_errors);
> +       stats->tx_dropped = atomic_long_read(&vport->err_stats.tx_dropped);
> +       stats->rx_dropped = atomic_long_read(&vport->err_stats.rx_dropped);
>
>         for_each_possible_cpu(i) {
>                 const struct pcpu_sw_netstats *percpu_stats;
> @@ -495,27 +489,24 @@ int ovs_vport_send(struct vport *vport, struct sk_buff *skb)
>  static void ovs_vport_record_error(struct vport *vport,
>                                    enum vport_err_type err_type)
>  {
> -       spin_lock(&vport->stats_lock);
> -
>         switch (err_type) {
>         case VPORT_E_RX_DROPPED:
> -               vport->err_stats.rx_dropped++;
> +               atomic_long_inc(&vport->err_stats.rx_dropped);
>                 break;
>
>         case VPORT_E_RX_ERROR:
> -               vport->err_stats.rx_errors++;
> +               atomic_long_inc(&vport->err_stats.rx_errors);
>                 break;
>
>         case VPORT_E_TX_DROPPED:
> -               vport->err_stats.tx_dropped++;
> +               atomic_long_inc(&vport->err_stats.tx_dropped);
>                 break;
>
>         case VPORT_E_TX_ERROR:
> -               vport->err_stats.tx_errors++;
> +               atomic_long_inc(&vport->err_stats.tx_errors);
>                 break;
>         }
>
> -       spin_unlock(&vport->stats_lock);
>  }
>
>  static void free_vport_rcu(struct rcu_head *rcu)
> diff --git a/net/openvswitch/vport.h b/net/openvswitch/vport.h
> index 35f89d8..0d95b9f 100644
> --- a/net/openvswitch/vport.h
> +++ b/net/openvswitch/vport.h
> @@ -62,10 +62,10 @@ int ovs_vport_send(struct vport *, struct sk_buff *);
>  /* The following definitions are for implementers of vport devices: */
>
>  struct vport_err_stats {
> -       u64 rx_dropped;
> -       u64 rx_errors;
> -       u64 tx_dropped;
> -       u64 tx_errors;
> +       atomic_long_t rx_dropped;
> +       atomic_long_t rx_errors;
> +       atomic_long_t tx_dropped;
> +       atomic_long_t tx_errors;
>  };
>  /**
>   * struct vport_portids - array of netlink portids of a vport.
> @@ -93,7 +93,6 @@ struct vport_portids {
>   * @dp_hash_node: Element in @datapath->ports hash table in datapath.c.
>   * @ops: Class structure.
>   * @percpu_stats: Points to per-CPU statistics used and maintained by vport
> - * @stats_lock: Protects @err_stats;
>   * @err_stats: Points to error statistics used and maintained by vport
>   */
>  struct vport {
> @@ -108,7 +107,6 @@ struct vport {
>
>         struct pcpu_sw_netstats __percpu *percpu_stats;
>
> -       spinlock_t stats_lock;
>         struct vport_err_stats err_stats;
>  };
>
> --
> 1.7.10.4
>
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