> -----Original Message-----
> From: Darrell Ball [mailto:[email protected]]
> Sent: Friday, August 25, 2017 6:19 PM
> To: Fischetti, Antonio <[email protected]>; [email protected]
> Subject: Re: [ovs-dev] [PATCH v4] dpif-netdev: Avoid reading RSS hash when EMC
> is disabled
>
> Hi Antonio
>
> On 8/25/17, 6:56 AM, "[email protected] on behalf of
> [email protected]" <[email protected] on behalf of
> [email protected]> wrote:
>
> When EMC is disabled the reading of RSS hash is skipped.
> Also, for packets that are not recirculated it retrieves
> the hash value without considering the recirc id.
>
> Signed-off-by: Antonio Fischetti <[email protected]>
> ---
>
> V4
> - reworked to remove dependencies from other patches in
> patchset "Skip EMC for recirc pkts and other optimizations."
> https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__mail.openvswitch.org_pipermail_ovs-2Ddev_2017-
> 2DAugust_337320.html&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=BVhFA09CGX7JQ5Ih-
> uZnsw&m=7UGZunJeutRugFmidRAykhZFRYscZ2rUUmhF7Ys9IM8&s=hzVGT1bI3zOj_x9J5cu18Q2D5
> WLHdEC1qhQ-Gu--TEE&e=
>
> - measurements were repeated with the latest head of master.
>
> Port-to-Port Test
> =================
> Software built with "-O2 -march=native -g".
>
> I measured the Rx rate regardless of pkt loss by sending 1 UDP
> flow,
> 64B packets, at the line-rate.
>
> 2 PMDs with 3 Tx queues.
>
> Flows setup:
> in_port=dpdk0 actions=output:dpdk1
> in_port=dpdk1 actions=output:dpdk0
>
> Results
> -------
> Values are for the Rx rate in Mpps, regardless of packet loss.
>
> RSS column:
> Yes: RSS hash is provided by the NIC
> No: RSS is disabled and the 5-tuple hash must be
> computed in software.
>
> Note: to simulate RSS disabled I added the line
> dp_packet_rss_valid(struct dp_packet *p)
> {
> +return false;
> #ifdef DPDK_NETDEV
>
> EMC column:
> Yes: default probability insertion,
> No: EMC disabled.
>
> Orig means Commit ID:
> 75f9e007e7f7eb91461e238f882d1c539c56bb8d
>
> [Darrell]
> It looks like the main benefit (+6% throughput) occurs
> when RSS is not calculated by the NIC and emc is disabled. What are the common
> cases when RSS is not generated by the NIC ?
[Antonio]
A common case could be when packets are coming in from a VM.
Also when the NIC does not provide a hash value, but this shouldn't be
considered a common case I guess.
>
>
>
> +--------------+----------------+
> +-----+-----+ Orig | Orig + this |
> | RSS | EMC | | patch |
> +-----+-----+--------------+----------------+
> | Yes | Yes | 12.02, 11.38 | 12.18, 11.32 |
> | Yes | No | 8.35, 8.36 | 8.36, 8.38 |
> +-----+-----+--------------+----------------+
> | No | Yes | 9.91, 11.15 | 9.84, 11.08 |
> | No | No | 7.83, 7.87 | 8.33, 8.35 |
> +-----+-----+--------------+----------------+
>
> ---
> lib/dpif-netdev.c | 32 ++++++++++++++++++++++++++++----
> 1 file changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index e2cd931..1157998 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -4567,6 +4567,22 @@ dp_netdev_upcall(struct dp_netdev_pmd_thread *pmd,
> struct dp_packet *packet_,
> }
>
> static inline uint32_t
> +dpif_netdev_packet_get_rss_hash_orig_pkt(struct dp_packet *packet,
> + const struct miniflow *mf)
> +{
> + uint32_t hash;
> +
> + if (OVS_LIKELY(dp_packet_rss_valid(packet))) {
> + hash = dp_packet_get_rss_hash(packet);
> + } else {
> + hash = miniflow_hash_5tuple(mf, 0);
> + dp_packet_set_rss_hash(packet, hash);
> + }
> +
> + return hash;
> +}
> +
> +static inline uint32_t
> dpif_netdev_packet_get_rss_hash(struct dp_packet *packet,
> const struct miniflow *mf)
> {
> @@ -4701,10 +4717,18 @@ emc_processing(struct dp_netdev_pmd_thread *pmd,
> }
> miniflow_extract(packet, &key->mf);
> key->len = 0; /* Not computed yet. */
> - key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
> -
> - /* If EMC is disabled skip emc_lookup */
> - flow = (cur_min == 0) ? NULL: emc_lookup(flow_cache, key);
> + /* If EMC is disabled skip hash computation and emc_lookup */
> + if (OVS_LIKELY(cur_min)) {
> + if (!md_is_valid) {
> + key->hash =
> dpif_netdev_packet_get_rss_hash_orig_pkt(packet,
> + &key->mf);
> + } else {
> + key->hash = dpif_netdev_packet_get_rss_hash(packet, &key-
> >mf);
> + }
> + flow = emc_lookup(flow_cache, key);
> + } else {
> + flow = NULL;
> + }
> if (OVS_LIKELY(flow)) {
> dp_netdev_queue_batches(packet, flow, &key->mf, batches,
> n_batches);
> --
> 2.4.11
>
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