[ovs-dev] [PATCH v3] dpcls: Avoid one 8-byte chunk in subtable mask.

[Jarno Rajahalme]

Thanks for the update! Pushed to master with small edits for clarification.

  Jarno


> On Jan 6, 2017, at 1:45 AM, antonio.fischetti at intel.com wrote:
> 
> This patch allows to skip the chunk comprising of dp_hash and in_port
> in the subtable mask when the packet is not recirculated.  This will
> slightly speed up the hash computation as one expensive function call
> to hash_add64() can be skipped.
> For each new netdev flow we wildcard in_port in the mask, so in the
> physical case where dp_hash is also wildcarded, the resulting 8-byte
> chunk will not be part of the subtable mask.
> 
> The idea behind is that all the packets within a given dpcls will
> have the same in_port value and typically dp_hash == 0.  So they will
> have the same 8-bytes chunk in their {dp_hash, in_port} portion of the
> miniflow. This doesn't contribute effectively in spreading hash values
> and avoiding collisions.
> 
> v2: Using ovs_assert.
> v3: Fix for dumped flows missing the in_port match.
> 
> Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
> Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> Co-authored-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
> Signed-off-by: Jarno Rajahalme <jarno at ovn.org>
> Co-authored-by: Jarno Rajahalme <jarno at ovn.org>
> ---
> lib/dpif-netdev.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
> 
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 1a47a45..4425f85 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -2120,6 +2120,9 @@ dp_netdev_flow_to_dpif_flow(const struct dp_netdev_flow *netdev_flow,
>         };
> 
>         miniflow_expand(&netdev_flow->cr.mask->mf, &wc.masks);
> +        /* in_port is exact matched, but we have left it out from the mask for
> +         * optimization reasons.  Add in_port back to the mask. */
> +        wc.masks.in_port.odp_port = ODPP_NONE;
> 
>         /* Key */
>         offset = key_buf->size;
> @@ -2278,7 +2281,17 @@ dp_netdev_flow_add(struct dp_netdev_pmd_thread *pmd,
>     struct dpcls *cls;
>     odp_port_t in_port = match->flow.in_port.odp_port;
> 
> +    /* As we select the dpcls based on the port number, each netdev flow
> +     * belonging to the same dpcls will have the same odp_port value.
> +     * For performance reasons here we wildcard odp_port in the mask.  In the
> +     * physical case where dp_hash is also wildcarded, the resulting 8-byte
> +     * chunk {dp_hash, in_port} will be ignored by netdev_flow_mask_init() and
> +     * will not be part of the subtable mask.
> +     * This will speed up the hash computation during dpcls_lookup() because
> +     * one call to hash_add64() will be skipped. */
> +    match->wc.masks.in_port.odp_port = 0;
>     netdev_flow_mask_init(&mask, match);
> +    match->wc.masks.in_port.odp_port = ODPP_NONE;
>     /* Make sure wc does not have metadata. */
>     ovs_assert(!FLOWMAP_HAS_FIELD(&mask.mf.map, metadata)
>                && !FLOWMAP_HAS_FIELD(&mask.mf.map, regs));
> -- 
> 2.4.11
>