[ovs-dev] [PATCH v2] odp-execute: Reuse rss hash in OVS_ACTION_ATTR_HASH.

[Ilya Maximets]

On 18.07.2017 06:48, Darrell Ball wrote:
> 
> 
> On 7/13/17, 8:07 AM, "ovs-dev-bounces at openvswitch.org on behalf of Ilya Maximets" <ovs-dev-bounces at openvswitch.org on behalf of i.maximets at samsung.com> wrote:
> 
>     If RSS hash exists in a packet it can be reused instead of
>     5 tuple hash re-calculation in OVS_ACTION_ATTR_HASH. This
>     leads to increasing the performance of sending packets to
>     the OVS bonding in userspace datapath up to 10-15%.
>     
>     Additionally fixed unit test 'select group with dp_hash
>     selection method' to not depend on dp_hash value.
>     
>     Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
>     ---
>     
>     Version 2:
>     	* Removed assumption on hash_basis value.
>     	* hash_finish replaced with hash_int as more appropriate.
>     	* Fixed 'select group with dp_hash selection method' UT.
>     
>      lib/odp-execute.c     | 11 +++++++++--
>      tests/ofproto-dpif.at |  4 ++--
>      2 files changed, 11 insertions(+), 4 deletions(-)
>     
>     diff --git a/lib/odp-execute.c b/lib/odp-execute.c
>     index d656334..03120bf 100644
>     --- a/lib/odp-execute.c
>     +++ b/lib/odp-execute.c
>     @@ -646,8 +646,15 @@ odp_execute_actions(void *dp, struct dp_packet_batch *batch, bool steal,
>                      uint32_t hash;
>      
>                      DP_PACKET_BATCH_FOR_EACH (packet, batch) {
>     -                    flow_extract(packet, &flow);
>     -                    hash = flow_hash_5tuple(&flow, hash_act->hash_basis);
>     +                    /* RSS hash can be used here instead of 5tuple for
>     +                     * performance reasons. */
>     +                    if (dp_packet_rss_valid(packet)) {
>     +                        hash = dp_packet_get_rss_hash(packet);
>     +                        hash = hash_int(hash, hash_act->hash_basis);
>     +                    } else {
>     +                        flow_extract(packet, &flow);
>     +                        hash = flow_hash_5tuple(&flow, hash_act->hash_basis);
>     +                    }
> 
> Presently, OVS does not have configurable hashing fields for bonds, although this seems to be asked for.
> Also, OVS does not have symmetrical hashing for bonding, as exists for the multipath action.
> If/when these features are added, taking the RSS of various input interfaces to hash across the outgoing members of
> a given bond would not automatically work since a flexible hash algorithm would not be easily configured the same
> across different input devices and also enforcing symmetry would be similarly difficult.
> Potentially, we could also make these features mutually exclusive with using the RSS hash as is done here.
> 
> This patch does offer some performance gain, so we could revisit as needed in the above cases ?

For configurable hashing fields, I think, there should be different OVS_HASH_ALG type.
Symmetric hashing is also not required for bonding to work correctly.
>From the other side kernel datapath uses exactly same thing to execute OVS_ACTION_ATTR_HASH.
skb_get_hash() is used there which is equal to RSS hash if it available.
So, this patch just unifies kernel and userspace ways to execute hash actions.
If some additional characteristics will be required we will modify both datapaths accordingly.

Best regards, Ilya Maximets.

>                          packet->md.dp_hash = hash;
>                      }
>                  } else {
>     diff --git a/tests/ofproto-dpif.at b/tests/ofproto-dpif.at
>     index 8373f90..83c72cf 100644
>     --- a/tests/ofproto-dpif.at
>     +++ b/tests/ofproto-dpif.at
>     @@ -491,10 +491,10 @@ for d in 0 1 2 3 4 5 6 7 8 9 a b c d e f; do
>          AT_CHECK([ovs-appctl netdev-dummy/receive p1 $pkt])
>      done
>      
>     -AT_CHECK([ovs-appctl dpctl/dump-flows | sed 's/dp_hash(.*\/0x1)/dp_hash(0xXXXX\/0x1)/' | strip_ufid | strip_used | sort], [0], [dnl
>     +AT_CHECK([ovs-appctl dpctl/dump-flows | sed 's/dp_hash(.*\/0x1)/dp_hash(0xXXXX\/0x1)/' | sed 's/\(actions:1\)[[01]]/\1X/' | strip_ufid | strip_used | sort], [0], [dnl
>      flow-dump from non-dpdk interfaces:
>      recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(src=192.168.0.1,frag=no), packets:15, bytes:630, used:0.0s, actions:hash(hash_l4(0)),recirc(0x2)
>     -recirc_id(0x2),dp_hash(0xXXXX/0x1),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:15, bytes:630, used:0.0s, actions:11
>     +recirc_id(0x2),dp_hash(0xXXXX/0x1),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:15, bytes:630, used:0.0s, actions:1X
>      ])
>      
>      OVS_VSWITCHD_STOP
>     -- 
>     2.7.4
>     
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