VPP main thread blocked by DPDK APIs

[Stephen Hemminger]

On Wed, 22 Dec 2021 08:25:49 +0000
Ruitao Gong <ruitao.gong at mavenir.com> wrote:

> hi DEVers,
> 
> Send this mail for some help about VPP and DPDK.
> rte_eth_stats_get (xd->port_id, &xd->stats)
> rte_eth_xstats_get (xd->port_id, xd->xstats, len)
>     APIs in dpdk_update_counters() node "dpdk_process" will cost about 140ms each physical interface every 10s (DPDK_STATS_POLL_INTERVAL).
>     main_thread will blocked N*140 ms when N physical interface in up state.
>     if govpp send heartbeat message to VPP, main_thread will have chance delay to read msg and reply, when main_thread blocked by doing update_counters.
>     link between GoVPP and VPP will turn down when delay time more than 250ms. It is easy to reproduce the scenario.
>     is there any plan to fix it or some suggestion to avoid it? Many thanks!
> 
> env details:
>     GoVPP:v0.3.5
>     DPDK version: 20.05
>     VPP version:20.09
>     centos7 + Intel X710
> expansion-rom-version:
> bus-info: 0000:19:00.0
> supports-statistics: yes
> supports-test: yes
> supports-eeprom-access: yes
> supports-register-dump: yes
> supports-priv-flags: yes
> 
>     startup.conf dpdk uio-driver vfio_pci
>     driver: i40evf version: 3.2.2-k
> 
> B&R,
> Ruitao

Polling for statistics may be expensive based on the hardware, it requires the device driver
to query the hardware for each queue. These requests may involve setting a flag and polling
for completion of the request.

We had similar issues, with bnxt; ended up doing small changes to driver to avoid
polling for queue information for unused queues and that helped. But getting statistics
can be still be too expensive.


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