Re: GCP cloud : Virtio-PMD performance Issue

[Mukul Sinha <mukul.sinha@broadcom.com>]

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Thanks Maxime,
We will analyse further and try pinpointing the regression commit between
DPDK-21.11 & DPDK-21.08.
Will get back with further queries once we have an update.

On Fri, Dec 13, 2024 at 4:17 PM Maxime Coquelin <maxime.coquelin@redhat.com>
wrote:

> (with DPDK ML that got removed)
>
> On 12/13/24 11:46, Maxime Coquelin wrote:
> >
> >
> > On 12/13/24 11:21, Mukul Sinha wrote:
> >> Thanks @joshwash@google.com <mailto:joshwash@google.com> @Maxime
> >> Coquelin <mailto:maxime.coquelin@redhat.com> for the inputs.
> >>
> >> @Maxime Coquelin <mailto:maxime.coquelin@redhat.com>
> >> I did code bisecting and was able to pin-point through test-pmd run
> >> that *this issue we are starting to see since DPDK-21.11 version
> >> onwards. Till DPDK-21.08 this issue is not seen.*
> >> To remind the issue what we see is that while actual amount of
> >> serviced traffic by the hypervisor remains almost same between the two
> >> versions (implying the underlying GCP hypervisor is only capable of
> >> handling that much) but in >=dpdk-21.11 versions the virtio-PMD is
> >> pushing almost 20x traffic compared to dpdk-21.08 (This humongous
> >> traffic rate in  >=dpdk-21.11 versions leads to high packet drop rates
> >> since the underlying hypervisor is only capable of max handling the
> >> same load it was servicing in <=dpdk-21.08)
> >> The same pattern can be seen even if we run traffic for a longer
> >> duration.
> >>
> >> *_Eg:_*
> >> Testpmd traffic run (for packet-size=1518) for exact same
> >> time-interval of 15 seconds:
> >>
> >> _*>=21.11 DPDK version*_
> >>    ---------------------- Forward statistics for port 0
> >>   ----------------------
> >>    RX-packets: 2              RX-dropped: 0             RX-total: 2
> >>    TX-packets: 19497570 *TX-dropped: 364674686 *    TX-total: 384172256
> >>
> ----------------------------------------------------------------------------
> >> _*Upto 21.08 DPDK version *_
> >>    ---------------------- Forward statistics for port 0
> >>   ----------------------
> >>    RX-packets: 3              RX-dropped: 0             RX-total: 3
> >>    TX-packets: 19480319       TX-dropped: 0             TX-total:
> >> 19480319
> >>
> ----------------------------------------------------------------------------
> >>
> >> As you can see
> >>  >=dpdk-21.11
> >> Packets generated : 384 million Packets serviced : ~19.5 million :
> >> Tx-dropped : 364 million
> >> <=dpdk-21.08
> >> Packets generated : ~19.5 million Packets serviced : ~19.5 million :
> >> Tx-dropped : 0
> >>
> >>
> ==========================================================================
> >> @Maxime Coquelin <mailto:maxime.coquelin@redhat.com>
> >> I have run through all the commits made by virtio-team between
> >> DPDK-21.11 and DPDK-21.08 as per the commit-logs available at
> >> https://git.dpdk.org/dpdk/log/drivers/net/virtio
> >> <https://git.dpdk.org/dpdk/log/drivers/net/virtio>
> >> I even tried undoing all the possible relevant commits (I could think
> >> of) on a dpdk-21.11 workspace & then re-running testpmd in order to
> >> track down which commit has introduced this regression but no luck.
> >> Need your inputs further if you could glance through the commits made
> >> in between these releases and let us know if there's any particular
> >> commit of interest which you think can cause the behavior as seen
> >> above (or if there's any commit not captured in the above git link;
> >> maybe a commit checkin outside the virtio PMD code perhaps?).
> >
> > As your issue seems 100% reproducible, using git bisect you should be
> > able to point to the commit introducing the regression.
> >
> > This is what I need to be able to help you.
> >
> > Regards,
> > Maxime
> >
> >>
> >> Thanks,
> >> Mukul
> >>
> >>
> >> On Mon, Dec 9, 2024 at 9:54 PM Joshua Washington <joshwash@google.com
> >> <mailto:joshwash@google.com>> wrote:
> >>
> >>     Hello,
> >>
> >>     Based on your VM shape (8 vcpu VM) and packet size (1518B packets),
> >>     what you are seeing is exactly expected. 8 vCPU Gen 2 VMs has a
> >>     default egress cap of 16 Gbps. This equates to roughly 1.3Mpps when
> >>     using 1518B packets, including IFG. Over the course of 15 seconds,
> >>     19.5 million packets should be sent, which matches both cases. The
> >>     difference here seems to be what happens on DPDK, not GCP. I don't
> >>     believe that packet drops on the host NIC are captured in DPDK
> >>     stats; likely the descriptor ring just filled up because the egress
> >>     bandwidth cap was hit and queue servicing was throttled. This would
> >>     cause a TX burst to return less packets than the burst size. The
> >>     difference between 20.05 and 22.11 might have to do with this
> >>     reporting, or a change in testpmd logic for when to send new bursts
> >>     of traffic.
> >>
> >>     Best,
> >>     Josh
> >>
> >>
> >>     On Mon, Dec 9, 2024, 07:39 Mukul Sinha <mukul.sinha@broadcom.com
> >>     <mailto:mukul.sinha@broadcom.com>> wrote:
> >>
> >>         GCP-dev team
> >>         @jeroendb@google.com
> >>         <mailto:jeroendb@google.com>@rushilg@google.com
> >>         <mailto:rushilg@google.com> @joshwash@google.com
> >>         <mailto:joshwash@google.com>
> >>         Can you please check the following email & get back ?
> >>
> >>
> >>         On Fri, Dec 6, 2024 at 2:04 AM Mukul Sinha
> >>         <mukul.sinha@broadcom.com <mailto:mukul.sinha@broadcom.com>>
> >> wrote:
> >>
> >>             Hi GCP & Virtio-PMD dev teams,
> >>             We are from VMware NSX Advanced Load Balancer Team whereby
> >>             in GCP-cloud (*custom-8-8192 VM instance type 8core8G*) we
> >>             are triaging an issue of TCP profile application throughput
> >>             performance with single dispatcher core single Rx/Tx queue
> >>             (queue depth: 2048) the throughput performance we get using
> >>             dpdk-22.11 virtio-PMD code is degraded significantly when
> >>             compared to when using dpdk-20.05 PMD
> >>             We see high amount of Tx packet drop counter incrementing on
> >>             virtio-NIC pointing to issue that the GCP hypervisor side is
> >>             unable to drain the packets faster (No drops are seen on Rx
> >>             side)
> >>             The behavior is like this :
> >>             _Using dpdk-22.11_
> >>             At 75% CPU usage itself we start seeing huge number of Tx
> >>             packet drops reported (no Rx drops) causing TCP
> >>             restransmissions eventually bringing down the effective
> >>             throughput numbers
> >>             _Using dpdk-20.05_
> >>             even at ~95% CPU usage without any packet drops (neither Rx
> >>             nor Tx) we are able to get a much better throughput
> >>
> >>             To improve performance numbers with dpdk-22.11 we have tried
> >>             increasing the queue depth to 4096 but that din't help.
> >>             If with dpdk-22.11 we move from single core Rx/Tx queue=1 to
> >>             single core Rx/Tx queue=2 we are able to get slightly better
> >>             numbers (but still doesnt match the numbers obtained using
> >>             dpdk-20.05 single core Rx/Tx queue=1). This again
> >>             corroborates the fact the GCP hypervisor is the bottleneck
> >>             here.
> >>
> >>             To root-cause this issue we were able to replicate this
> >>             behavior using native DPDK testpmd as shown below (cmds
> >> used):-
> >>             Hugepage size: 2 MB
> >>               ./app/dpdk-testpmd -l 0-1 -n 1 -- -i --nb-cores=1
> >>             --txd=2048 --rxd=2048 --rxq=1 --txq=1  --portmask=0x3
> >>             set fwd mac
> >>             set fwd flowgen
> >>             set txpkts 1518
> >>             start
> >>             stop
> >>
> >>             Testpmd traffic run (for packet-size=1518) for exact same
> >>             time-interval of 15 seconds:
> >>
> >>             _22.11_
> >>                ---------------------- Forward statistics for port 0
> >>               ----------------------
> >>                RX-packets: 2              RX-dropped: 0
> >> RX-total: 2
> >>                TX-packets: 19497570 *TX-dropped: 364674686 *
> >>             TX-total: 384172256
> >>
> >>
> ----------------------------------------------------------------------------
> >>             _20.05_
> >>                ---------------------- Forward statistics for port 0
> >>               ----------------------
> >>                RX-packets: 3              RX-dropped: 0
> >> RX-total: 3
> >>                TX-packets: 19480319       TX-dropped: 0
> >> TX-total: 19480319
> >>
> >>
> ----------------------------------------------------------------------------
> >>
> >>             As you can see
> >>             dpdk-22.11
> >>             Packets generated : 384 million Packets serviced : ~19.5
> >>             million : Tx-dropped : 364 million
> >>             dpdk-20.05
> >>             Packets generated : ~19.5 million Packets serviced : ~19.5
> >>             million : Tx-dropped : 0
> >>
> >>             Actual serviced traffic remains almost same between the two
> >>             versions (implying the underlying GCP hypervisor is only
> >>             capable of handling that much) but in dpdk-22.11 the PMD is
> >>             pushing almost 20x traffic compared to dpdk-20.05
> >>             The same pattern can be seen even if we run traffic for a
> >>             longer duration.
> >>
> >>
> ===============================================================================================
> >>
> >>             Following are our queries:
> >>             @ Virtio-dev team
> >>             1. Why in dpdk-22.11 using virtio PMD the testpmd
> >>             application is able to pump 20 times Tx traffic towards
> >>             hypervisor compared to dpdk-20.05 ?
> >>             What has changed either in the virtio-PMD or in the
> >>             virtio-PMD & underlying hypervisor communication causing
> >>             this behavior ?
> >>             If you see actual serviced traffic by the hypervisor remains
> >>             almost on par with dpdk-20.05 but its the humongous packets
> >>             drop count which can be overall detrimental for any
> >>             DPDK-application running TCP traffic profile.
> >>             Is there a way to slow down the number of packets sent
> >>             towards the hypervisor (through either any code change in
> >>             virtio-PMD or any config setting) and make it on-par with
> >>             dpdk-20.05 performance ?
> >>             2. In the published Virtio performance report Release 22.11
> >>             we see no qualification of throughput numbers done on
> >>             GCP-cloud. Is there any internal performance benchmark
> >>             numbers you have for GCP-cloud and if yes can you please
> >>             share it with us so that we can check if there's any
> >>             configs/knobs/settings you used to get optimum performance.
> >>
> >>             @ GCP-cloud dev team
> >>             As we can see any amount of traffic greater than what can be
> >>             successfully serviced by the GCP hypervisor is all getting
> >>             dropped hence we need help from your side to reproduce this
> >>             issue in your in-house setup preferably using the same VM
> >>             instance type as highlighted before.
> >>             We need further investigation by you from the GCP host level
> >>             side to check on parameters like running out of Tx buffers
> >>             or Queue full conditions for the virtio-NIC or number of NIC
> >>             Rx/Tx kernel threads as to what is causing hypervisor to not
> >>             match up to the traffic load pumped in dpdk-22.11
> >>             Based on your debugging we would additionally need inputs as
> >>             to what can be tweaked or any knobs/settings can be
> >>             configured from the GCP-VM level to get better performance
> >>             numbers.
> >>
> >>             Please feel free to reach out to us for any further queries.
> >>
> >>             _Additional outputs for debugging:_
> >>             lspci | grep Eth
> >>             00:06.0 Ethernet controller: Red Hat, Inc. Virtio network
> >> device
> >>             root@dcg15-se-ecmyw:/home/admin/dpdk/build# ethtool -i eth0
> >>             driver: virtio_net
> >>             version: 1.0.0
> >>             firmware-version:
> >>             expansion-rom-version:
> >>             bus-info: 0000:00:06.0
> >>             supports-statistics: yes
> >>             supports-test: no
> >>             supports-eeprom-access: no
> >>             supports-register-dump: no
> >>             supports-priv-flags: no
> >>
> >>             testpmd> show port info all
> >>             ********************* Infos for port 0
>  *********************
> >>             MAC address: 42:01:0A:98:A0:0F
> >>             Device name: 0000:00:06.0
> >>             Driver name: net_virtio
> >>             Firmware-version: not available
> >>             Connect to socket: 0
> >>             memory allocation on the socket: 0
> >>             Link status: up
> >>             Link speed: Unknown
> >>             Link duplex: full-duplex
> >>             Autoneg status: On
> >>             MTU: 1500
> >>             Promiscuous mode: disabled
> >>             Allmulticast mode: disabled
> >>             Maximum number of MAC addresses: 64
> >>             Maximum number of MAC addresses of hash filtering: 0
> >>             VLAN offload:
> >>                strip off, filter off, extend off, qinq strip off
> >>             No RSS offload flow type is supported.
> >>             Minimum size of RX buffer: 64
> >>             Maximum configurable length of RX packet: 9728
> >>             Maximum configurable size of LRO aggregated packet: 0
> >>             Current number of RX queues: 1
> >>             Max possible RX queues: 2
> >>             Max possible number of RXDs per queue: 32768
> >>             Min possible number of RXDs per queue: 32
> >>             RXDs number alignment: 1
> >>             Current number of TX queues: 1
> >>             Max possible TX queues: 2
> >>             Max possible number of TXDs per queue: 32768
> >>             Min possible number of TXDs per queue: 32
> >>             TXDs number alignment: 1
> >>             Max segment number per packet: 65535
> >>             Max segment number per MTU/TSO: 65535
> >>             Device capabilities: 0x0( )
> >>             Device error handling mode: none
> >>
> >>
> >>
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