netdev - Re: [ovs-dev] [PATCH v1] netdev: Make 100 percents packets sampled when sampling rate is 1.

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Message-ID: <CALnjE+qCbqtzMPHKV1M_HRdB+OTRCYsya3XuUeORJHn8E-jEjQ@mail.gmail.com>
Date:	Mon, 3 Aug 2015 11:18:00 -0700
From:	Pravin Shelar <pshelar@...ira.com>
To:	Wenyu Zhang <wenyuz@...are.com>
Cc:	Jesse Gross <jgross@...are.com>, netdev <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>
Subject: Re: [ovs-dev] [PATCH v1] netdev: Make 100 percents packets sampled
 when sampling rate is 1.

On Mon, Aug 3, 2015 at 12:11 AM, Wenyu Zhang <wenyuz@...are.com> wrote:
> When sampling rate is 1, the sampling probability is UINT32_MAX. The packet
> should be sampled even the prandom32() generate the number of UINT32_MAX.
> And none packet need be sampled when the probability is 0.
>
> Signed-off-by: Wenyu Zhang <wenyuz@...are.com>
> ---
>  net/openvswitch/actions.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index cf04c2f..03acb09 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -669,9 +669,11 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
>
>         for (a = nla_data(attr), rem = nla_len(attr); rem > 0;
>                  a = nla_next(a, &rem)) {
> +               uint32_t probability;
>                 switch (nla_type(a)) {
>                 case OVS_SAMPLE_ATTR_PROBABILITY:
> -                       if (prandom_u32() >= nla_get_u32(a))
> +                       probability = nla_get_u32(a);
> +                       if (!probability || probability > nla_get_u32(a))

This condition does not looks right to calculate sampling probability.
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