[ovs-dev] [PATCH] datapath: Correctly report flow used times for first 5 minutes after boot.

[Pravin Shelar]

On Fri, Feb 28, 2014 at 1:14 PM, Ben Pfaff <blp at nicira.com> wrote:
> The kernel starts out its "jiffies" timer as 5 minutes below zero, as
> shown in include/linux/jiffies.h:
>
>   /*
>    * Have the 32 bit jiffies value wrap 5 minutes after boot
>    * so jiffies wrap bugs show up earlier.
>    */
>   #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
>
> The loop in ovs_flow_stats_get() starts out with 'used' set to 0, then
> takes any "later" time.  This means that for the first five minutes after
> boot, flows will always be reported as never used, since 0 is greater than
> any time already seen.
>
> Signed-off-by: Ben Pfaff <blp at nicira.com>

Good catch.

Acked-by: Pravin B Shelar <pshelar at nicira.com>

> ---
>  datapath/flow.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/datapath/flow.c b/datapath/flow.c
> index c3e3fcb..e9a2a27 100644
> --- a/datapath/flow.c
> +++ b/datapath/flow.c
> @@ -1,5 +1,5 @@
>  /*
> - * Copyright (c) 2007-2013 Nicira, Inc.
> + * Copyright (c) 2007-2014 Nicira, Inc.
>   *
>   * This program is free software; you can redistribute it and/or
>   * modify it under the terms of version 2 of the GNU General Public
> @@ -148,7 +148,7 @@ void ovs_flow_stats_get(struct sw_flow *flow, struct ovs_flow_stats *ovs_stats,
>                          * block bottom-halves here.
>                          */
>                         spin_lock_bh(&stats->lock);
> -                       if (time_after(stats->used, *used))
> +                       if (!*used || time_after(stats->used, *used))
>                                 *used = stats->used;
>                         *tcp_flags |= stats->tcp_flags;
>                         ovs_stats->n_packets += stats->packet_count;
> --
> 1.7.10.4
>
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