> -----Original Message----- > From: Darrell Ball [mailto:[email protected]] > Sent: Wednesday, August 16, 2017 9:09 AM > To: Fischetti, Antonio <[email protected]>; [email protected] > Subject: Re: [ovs-dev] [PATCH v3 1/4] dpif-netdev: Skip EMC lookup/insert for > recirc packets > > > > -----Original Message----- > From: "Fischetti, Antonio" <[email protected]> > Date: Tuesday, August 15, 2017 at 6:55 AM > To: Darrell Ball <[email protected]>, "[email protected]" > <[email protected]> > Subject: RE: [ovs-dev] [PATCH v3 1/4] dpif-netdev: Skip EMC lookup/insert for > recirc packets > > > > > -----Original Message----- > > From: Darrell Ball [mailto:[email protected]] > > Sent: Monday, August 14, 2017 7:27 AM > > To: Fischetti, Antonio <[email protected]>; > [email protected] > > Subject: Re: [ovs-dev] [PATCH v3 1/4] dpif-netdev: Skip EMC > lookup/insert > for > > recirc packets > > > > > > > > -----Original Message----- > > From: <[email protected]> on behalf of > > "[email protected]" <[email protected]> > > Date: Friday, August 11, 2017 at 8:52 AM > > To: "[email protected]" <[email protected]> > > Subject: [ovs-dev] [PATCH v3 1/4] dpif-netdev: Skip EMC lookup/insert > for > > recirc packets > > > > When OVS is configured as a firewall, with thousands of active > > concurrent connections, the EMC gets quicly saturated and may > > come under heavy thrashing for the reason that original and > > recirculated packets keep overwriting the existing active EMC > > entries due to its limited size (8k). > > > > > > The recirculated packet could have been modified, in which case, maybe > we > > still want to do the emc lookup/insert ? > > [Antonio] > IMPO I'd say we should still skip emc anyway, because the purpose is to > mitigate thrashing when emc is full. So any recirculated packet should > be classified at the dpcls/ofproto layers. > I don't know if I'm missing something from your question? > > We can expect that a recirc pkt that has been modified - similarly to all > other recirculated pkts - could result in a miss when emc is full. > Later we should do an emc insertion that is likely to overwrite some > active entry. And recursively, this new insertion itself could be > overwritten - due to the shortage of locations - even before it is hit > again. This proposal is to mitigate the thrashing with the criteria of > reserving emc usage to original packets only. > So a limited resource like emc hopefully could be used more efficiently, > especially when there is more than 1 recirculation. > I guess that adding an exception for modified recirc pkts could also > drop a bit the throughtput as we should add another if statement inside > emc_processing. > > [Darrell] > I’ll can drop the edited packet case as my concern was really more general. > The concern is that recirculated packets should still be forwarded quickly if > possible > and using emc should help that. The first time through, emc is used for the > packet and then the second > time through, emc is not used, so it is slower. But, possibly the argument > could be made that since it is recirculated, > it is already slower, in which case, maybe a penalty for recirculated packets > is reasonable.
[Antonio] Agree. Other than that, in case of an emc congestion - eg a firewall with say 6,000 connections - with a lot of overwrites, the effect could be that a lot of lookups will fail and the new insertions are just overwriting active flows. This keeps a high failure for lookups and the continuous overwrites for insertions become an overhead. So in this case there's a penalty as for the original (ie the 1st time through) as for the recirculated packets. With this approach we are considering that with 6,000 flows we would need at least 12,000 entries with 1 recirculation. So one strategy to reduce thrashing could be to restrict emc usage to original packets only. The counterpart is that recirculated packets are slower, but the overall effect should be a benefit. > Instead of having a simple 50% black and white cutoff, maybe a penalty to the > insertion probability could be used ? [Antonio] Yes, at the beginning I was considering this solution. I then preferred the current one because it allows not only to skip insertions but also to skip lookups, especially when RSS hash must be computed in software. The check of the threshold - as this is happening inside emc_processing - is done with an '&' operation so to use as less cpu cycles as possible. > > > > > > > > This thrashing causes the EMC to be less efficient than the dcpls > > in terms of lookups and insertions. > > > > This patch allows to use the EMC efficiently by allowing only > > the 'original' packets to hit EMC. All recirculated packets are > > sent to the classifier directly. > > An empirical threshold EMC_RECIRCT_NO_INSERT_THRESHOLD - of 50% - > > for EMC occupancy is set to trigger this logic. By doing so when > > EMC utilization exceeds EMC_RECIRCT_NO_INSERT_THRESHOLD: > > - EMC Insertions are allowed just for original packets. > > EMC insertion and look up are skipped for recirculated packets. > > - Recirculated packets are sent to the classifier. > > > > This patch is based on patch > > "dpif-netdev: add EMC entry count and %full figure to > pmd-stats-show" > at: > > https://urldefense.proofpoint.com/v2/url?u=https- > > 3A__mail.openvswitch.org_pipermail_ovs-2Ddev_2017- > > > 2DJanuary_327570.html&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=BVhFA09CGX7JQ5Ih- > > uZnsw&m=NHY06RD-Bcweizxd86m6hcsLPKpe7a4WVSyh9aNZQlo&s=- > > PhWyltJ71UipVzd1D0H0I9k4uSTLdCJ_zanXxHd7fo&e= > > > > CC: Jan Scheurich <[email protected]> > > Signed-off-by: Antonio Fischetti <[email protected]> > > Signed-off-by: Bhanuprakash Bodireddy > <[email protected]> > > Co-authored-by: Bhanuprakash Bodireddy > <[email protected]> > > --- > > Connection Tracker testbench set up with > > > > table=0, priority=1 actions=drop > > table=0, priority=10,arp actions=NORMAL > > table=0, priority=100,ct_state=-trk,ip actions=ct(table=1) > > table=1, ct_state=+new+trk,ip,in_port=1 actions=ct(commit),output:2 > > table=1, ct_state=+est+trk,ip,in_port=1 actions=output:2 > > table=1, ct_state=+new+trk,ip,in_port=2 actions=drop > > table=1, ct_state=+est+trk,ip,in_port=2 actions=output:1 > > > > 2 PMDs, 3 Tx queues. > > > > I measured packet Rx rate (regardless of packet loss). Bidirectional > > test with 64B UDP packets. > > Each row is a test with a different number of traffic streams. The > traffic > > generator is set so that each stream establishes one UDP connection. > > Mpps columns reports the Rx rates on the 2 sides. > > > > I set up the generator to loop on the dest IP addr on one side, > > and loop instead on the source IP addr on the other side. > > > > For example to generate 10 different flows, I was sending to phy > port > #1 > > UDP, IPsrc:10.10.10.10, IPdest: 20.20.20.[20-29], PortSrc: 63, > PortDest: 63 > > > > Instead to phy port #2 (source and dest IPs are now swapped): > > UDP, IPsrc: 20.20.20.[20-29], IPdest: 10.10.10.10, PortSrc: 63, > PortDest: > > 63 > > > > I saw the following performance improvement. > > > > Original OvS-DPDK means at Commit ID: > > 6b1babacc3ca0488e07596bf822fe356c9bab646 > > > > +----------------------+-----------------------+ > > | Original OvS-DPDK | Original OvS-DPDK | > > | | + this patch | > > ---------+------------+---------+------------+----------+ > > Traffic | Rx | EMC | Rx | EMC | > > Streams | [Mpps] | entries | [Mpps] | entries | > > ---------+------------+---------+------------+----------+ > > 100 | 2.43, 2.49 | 200 | 2.55, 2.57 | 201 | > > 1,000 | 2.01, 2.02 | 2007 | 2.12, 2.12 | 2006 | > > 2,000 | 1.93, 1.95 | 3868 | 1.98, 1.96 | 3884 | > > 3,000 | 1.87, 1.91 | 5086 | 1.97, 1.97 | 4757 | > > 4,000 | 1.83, 1.82 | 6173 | 1.94, 1.93 | 5280 | > > 10,000 | 1.67, 1.69 | 7826 | 1.82, 1.81 | 7090 | > > 30,000 | 1.57, 1.59 | 8192 | 1.66, 1.67 | 8192 | > > ---------+------------+---------+------------+----------+ > > > > This test setup implies 1 recirculation on each received packet. > > We didn't check this patch in a test scenario where more than 1 > > recirculation is occurring per packet. > > --- > > lib/dpif-netdev.c | 65 > > +++++++++++++++++++++++++++++++++++++++++++++++++++---- > > 1 file changed, 61 insertions(+), 4 deletions(-) > > > > diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c > > index bea1c3f..8f6b96b 100644 > > --- a/lib/dpif-netdev.c > > +++ b/lib/dpif-netdev.c > > @@ -4663,6 +4663,9 @@ dp_netdev_queue_batches(struct dp_packet *pkt, > > packet_batch_per_flow_update(batch, pkt, mf); > > } > > > > +/* Threshold to skip EMC for recirculated packets. */ > > +#define EMC_RECIRCT_NO_INSERT_THRESHOLD 0xFFFFF000 > > + > > /* Try to process all ('cnt') the 'packets' using only the exact > match > > cache > > * 'pmd->flow_cache'. If a flow is not found for a packet > 'packets[i]', > > the > > * miniflow is copied into 'keys' and the packet pointer is moved > at > the > > @@ -4714,8 +4717,36 @@ emc_processing(struct dp_netdev_pmd_thread > *pmd, > > 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); > > + /* > > + * EMC lookup is skipped when one or both of the following > > + * two cases occurs: > > + * > > + * - EMC is disabled. This is detected from cur_min. > > + * > > + * - The EMC occupancy exceeds > EMC_RECIRCT_NO_INSERT_THRESHOLD > > and > > + * the packet to be classified is being recirculated. > When > > this > > + * happens also EMC insertions are skipped for > recirculated > > + * packets. So that EMC is used just to store entries > which > > + * are hit from the 'original' packets. This way the > EMC > > + * thrashing is mitigated with a benefit on > performance. > > + */ > > + if (OVS_LIKELY(cur_min)) { > > + if (!md_is_valid) { > > + flow = emc_lookup(flow_cache, key); > > + } else { > > + /* Recirculated packet. */ > > + if (flow_cache->n_entries & > > EMC_RECIRCT_NO_INSERT_THRESHOLD) { > > + /* EMC occupancy is over the threshold. We > skip > EMC > > + * lookup for recirculated packets. */ > > + flow = NULL; > > + } else { > > + flow = emc_lookup(flow_cache, key); > > + } > > + } > > + } else { > > + flow = NULL; > > + } > > + > > if (OVS_LIKELY(flow)) { > > dp_netdev_queue_batches(packet, flow, &key->mf, > batches, > > n_batches); > > @@ -4800,7 +4831,20 @@ handle_packet_upcall(struct > dp_netdev_pmd_thread > > *pmd, > > add_actions->size); > > } > > ovs_mutex_unlock(&pmd->flow_mutex); > > - emc_probabilistic_insert(pmd, key, netdev_flow); > > + /* EMC insertion can be skipped by a probabilistic criteria > or > > + * - in case of recirculated packets - depending on the > number of > > + * EMC entries. */ > > + if (!packet->md.recirc_id) { > > + emc_probabilistic_insert(pmd, key, netdev_flow); > > + } else { > > + /* Recirculated packets. When EMC occupancy goes over > > + * a threshold we avoid inserting new entries. */ > > + if (!(pmd->flow_cache.n_entries & > > + EMC_RECIRCT_NO_INSERT_THRESHOLD)) { > > + /* Still under the threshold. */ > > + emc_probabilistic_insert(pmd, key, netdev_flow); > > + } > > + } > > } > > } > > > > @@ -4893,7 +4937,20 @@ fast_path_processing(struct > dp_netdev_pmd_thread > > *pmd, > > > > flow = dp_netdev_flow_cast(rules[i]); > > > > - emc_probabilistic_insert(pmd, &keys[i], flow); > > + /* EMC insertion can be skipped by a probabilistic criteria > or > > + * - in case of recirculated packets - depending on the > number of > > + * EMC entries. */ > > + if (!packet->md.recirc_id) { > > + emc_probabilistic_insert(pmd, &keys[i], flow); > > + } else { > > + /* Recirculated packets. When EMC occupancy goes over > > + * a threshold we avoid inserting new entries. */ > > + if (!(pmd->flow_cache.n_entries & > > + EMC_RECIRCT_NO_INSERT_THRESHOLD)) { > > + /* Still under the threshold. */ > > + emc_probabilistic_insert(pmd, &keys[i], flow); > > + } > > + } > > dp_netdev_queue_batches(packet, flow, &keys[i].mf, batches, > > n_batches); > > } > > > > -- > > 2.4.11 > > > > _______________________________________________ > > dev mailing list > > [email protected] > > https://urldefense.proofpoint.com/v2/url?u=https- > > 3A__mail.openvswitch.org_mailman_listinfo_ovs- > > 2Ddev&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=BVhFA09CGX7JQ5Ih- > uZnsw&m=NHY06RD- > > Bcweizxd86m6hcsLPKpe7a4WVSyh9aNZQlo&s=-xSW7voYnxrudlh_WPXXsKJ1n1o680- > > 3ZCuwj33q0H8&e= > > > > _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
