[ovs-dev] [PATCH] dpif-netdev: Check for PKT_RX_RSS_HASH flag.

[Traynor, Kevin]

> -----Original Message-----
> From: dev [mailto:dev-bounces at openvswitch.org] On Behalf Of Daniele Di
> Proietto
> Sent: Tuesday, June 16, 2015 7:39 PM
> To: dev at openvswitch.org
> Subject: [ovs-dev] [PATCH] dpif-netdev: Check for PKT_RX_RSS_HASH flag.
> 
> DPDK mbufs contain a valid RSS hash only if PKT_RX_RSS_HASH is
> set in 'ol_flags'.  Otherwise the hash is garbage and doesn't
> relate to the packet.
> 
> This fixes an issue with vhost, which, being a virtual NIC, doesn't
> compute the hash.
> 
> Unfortunately the ixgbe vPMD doesn't set the PKT_RX_RSS_HASH, forcing
> OVS to compute an hash is software.  This has a significant impact on
> performance (-30% throughput in a single flow setup) which can be
> mitigated in the CPU supports crc32c instructions.

Hi Daniele - revisiting this patch now that DPDK 2.1 support has been
integrated into OVS. I've checked and the ixgbe vector PMD correctly
sets the rss bit in ol_flags, so this patch should be able to do its
job now it will get the correct input. The patch still applies and LGTM.

> 
> Reported-by: Dongjun <dongj at dtdream.com>
> Suggested-by: Flavio Leitner <fbl at sysclose.org>
> Signed-off-by: Daniele Di Proietto <diproiettod at vmware.com>
> ---
>  lib/dp-packet.h   | 11 +++++++++++
>  lib/dpif-netdev.c |  2 +-
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/dp-packet.h b/lib/dp-packet.h
> index e4c2593..6840750 100644
> --- a/lib/dp-packet.h
> +++ b/lib/dp-packet.h
> @@ -529,11 +529,22 @@ dp_packet_set_rss_hash(struct dp_packet *p, uint32_t
> hash)
>  {
>  #ifdef DPDK_NETDEV
>      p->mbuf.hash.rss = hash;
> +    p->mbuf.ol_flags |= PKT_RX_RSS_HASH;
>  #else
>      p->rss_hash = hash;
>  #endif
>  }
> 
> +static inline bool
> +dp_packet_rss_valid(struct dp_packet *p)
> +{
> +#ifdef DPDK_NETDEV
> +    return p->mbuf.ol_flags & PKT_RX_RSS_HASH;
> +#else
> +    return true;
> +#endif
> +}
> +
>  #ifdef  __cplusplus
>  }
>  #endif
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index f13169c..c4a4b3a 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -3036,7 +3036,7 @@ dpif_netdev_packet_get_rss_hash(struct dp_packet
> *packet,
>  {
>      uint32_t hash, recirc_depth;
> 
> -    hash = dp_packet_get_rss_hash(packet);
> +    hash = dp_packet_rss_valid(packet) ? dp_packet_get_rss_hash(packet) : 0;
>      if (OVS_UNLIKELY(!hash)) {
>          hash = miniflow_hash_5tuple(mf, 0);
>          dp_packet_set_rss_hash(packet, hash);
> --
> 2.1.4
> 
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