[ovs-dev] [PATCH v2] dpcls: Avoid one 8-byte chunk in subtable mask.

[Jarno Rajahalme]

> On Jan 5, 2017, at 1:03 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.
> 

It appears you have not run the testsuite with this patch, as it consistently fails. This is due to dumped flows now missing the in_port match, which is caused by the subtable mask change. This can be fixed like this:

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 0b73056..5f6fc01 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -2098,6 +2098,9 @@ 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;

> 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
> 

Now there are two asserts for the same thing, I think the latter (the old one) should be removed.

  Jarno

> 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 | 11 +++++++++++
> 1 file changed, 11 insertions(+)
> 
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 1a47a45..68b434f 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -2278,7 +2278,18 @@ 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. */
> +    ovs_assert(match->wc.masks.in_port.odp_port == ODPP_NONE);
> +    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
>