DPDK22 issue: Unable to set more than 4 queues in Azure

[Nageswara Rao]

Issue is because of tap_mp_req_on_rxtx() sending msg.num_fds more
than RTE_MP_MAX_FD_NUM fds for queues > 4.
Looks like these tap driver changes are added as part of the below patch
http://patches.dpdk.org/project/dpdk/patch/20220121042944.23929-1-kumaraparamesh92@gmail.com/


On Mon, Jun 26, 2023 at 3:53 PM Nageswara Rao <nagpen75 at gmail.com> wrote:

> Yes, we are using vdev_netvsc. Native netvsc PMD we are observing issues
> in enabling multiple queues.
> Though we have 6 DPDK cores, unable to configure more than 4 queues.
>
> On Mon, Jun 26, 2023 at 12:18 AM Stephen Hemminger <
> stephen at networkplumber.org> wrote:
>
>> On Thu, 22 Jun 2023 22:06:10 +0530
>> Nageswara Rao <nagpen75 at gmail.com> wrote:
>>
>> > Hi All,
>> >
>> > We are observing the following issue with DPDK22.11. We didn’t find any
>> > upstream patches for this issue on the DPDK github. Is there any known
>> > issue, please let us know.
>> >
>> >
>> >
>> > *Issue:*
>> >
>> > On Azure platform, we are unable to configure more than 4 queues. When
>> we
>> > try to configure more than 4 queues its failing with “EAL: Cannot send
>> more
>> > than 8 FDs” error.
>> >
>> > Here I am pasting the working and failing testpmd logs.
>> >
>> > Please note that this issue is not observed in DPDK 21.11.
>> >
>>
>> You should be using the native netvsc PMD, not the
>> vdev_netvsc,failsafe,tap kludge.
>>
>> I don't work on Azure any more but I suspect the issue is that the default
>> in the kernel for TAP is for the number of queues == number of cores.
>>
>> You aren't going to see any real benefit from having more queues than
>> the number of DPDK cores.
>>
>>
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