On 8/25/17, 3:21 PM, "Fischetti, Antonio" <[email protected]> wrote:
> -----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-
>
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> 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.
Well, there is no pnic in this case.
I am thinking gateway usage is predominate in importance, but the RSS cases are
about equal
based on the sampling below, so we could almost ‘remove them from the
equation’, as it were.
For non-RSS:
Using emc, there is about 0.7 % degradation, but it is more common to use emc
So overall, it is not clear; what do you think ?
Also when the NIC does not provide a hash value, but this shouldn't be
considered a common case I guess.
I agree.
>
>
>
> +--------------+----------------+
> +-----+-----+ 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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