Re: mbufs getting reused despite nonzero refcnt (Alan Beadle)

[Fabio Fernandes <boicotinho@proton.me>]

Hi Alan,

Are you using RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE?
Drivers are not required to handle mbuf refcount when this flag is enabled.

Regards,
Fabio


Sent from Proton Mail Android


-------- Original Message --------
On 13/11/2024 08:00,  <users-request@dpdk.org> wrote:

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>     1. Re: mbufs getting reused despite nonzero refcnt (Alan Beadle)
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>  
>  ----------------------------------------------------------------------
>  
>  Message: 1
>  Date: Tue, 12 Nov 2024 08:02:06 -0500
>  From: Alan Beadle <ab.beadle@gmail.com>
>  To: Stephen Hemminger <stephen@networkplumber.org>
>  Cc: users@dpdk.org
>  Subject: Re: mbufs getting reused despite nonzero refcnt
>  Message-ID:
>  	<CANTAOdw6o6zWy3PC+Nq0cK2Skn1_5UwEX3j1=_=PziWUeR6VvA@mail.gmail.com>
>  Content-Type: text/plain; charset="UTF-8"
>  
>  Is there anything in the usage I described in my previous email which
>  might explain this problem? Is there anything else wrong with what I'm
>  doing driver-wise?
>  
>  On Sun, Nov 10, 2024 at 12:31?PM Alan Beadle <ab.beadle@gmail.com> wrote:
>  >
>  > I'm using the vfio-pci module with Intel X550-T2 NICs. I believe this
>  > means it will use the ixgbe driver? To be honest, I am a bit confused
>  > about the use of drivers in DPDK. I am using the first setup that I
>  > got to work and send/receive packets. Additional tips would be greatly
>  > appreciated. After loading the vfio-pci module I run dpdk-devbind.py
>  > --bind vfio-pci 65:00.1 and then I just use the standard DPDK API
>  > calls in my app. I was meaning to revisit this once my app was more
>  > complete.
>  >
>  > On Sun, Nov 10, 2024 at 12:12?PM Stephen Hemminger
>  > <stephen@networkplumber.org> wrote:
>  > >
>  > > On Sun, 10 Nov 2024 11:23:29 -0500
>  > > Alan Beadle <ab.beadle@gmail.com> wrote:
>  > >
>  > > > Hi everyone,
>  > > >
>  > > > I am using DPDK to send two-way traffic between a pair of machines. My
>  > > > application has local readers, remote acknowledgments, as well as
>  > > > automatic retries when a packet is lost. For these reasons I am using
>  > > > rte_mbuf_refcnt_update() to prevent the NIC from freeing the packet
>  > > > and recycling the mbuf before my local readers are done and the remote
>  > > > reader has acknowledged the message. I was advised to do this in an
>  > > > earlier thread on this mailing list.
>  > > >
>  > > > However, this does not seem to be working. After running my app for
>  > > > awhile and exchanging about 1000 messages in this way, my queue of
>  > > > unacknowledged mbufs is getting corrupted. The mbufs attached to my
>  > > > queue seem to contain data for newer messages than what is supposed to
>  > > > be in them, and in some cases contains a totally different type of
>  > > > packet (an acknack for instance). Obviously this results in retries of
>  > > > those messages failing to send the correct data and my application
>  > > > gets stuck.
>  > > >
>  > > > I have ensured that the refcount is not reaching 0. Each new mbuf
>  > > > immediately has the refcnt incremented by 1. I was concerned that
>  > > > retries might need the refcnt bumped again, but if I bump the refcount
>  > > > every time I resend a specific mbuf to the NIC, the refcounts just
>  > > > keep getting higher. So it looks like re-bumping it on a resend is not
>  > > > necessary.
>  > > >
>  > > > I have ruled out other possible explanations. The mbufs are being
>  > > > reused by rte_pktmbuf_alloc. I even tried playing with the EAL
>  > > > settings related to the number of mbuf descriptors and saw my changes
>  > > > directly correlate with how long it takes this problem to occur. How
>  > > > do I really prevent the driver from reusing packets that I still might
>  > > > need to resend?
>  > > >
>  > > > Thanks in advance,
>  > > > -Alan
>  > >
>  > > Which driver, could be a driver bug.
>  > >
>  > > Also, you should be able to trace mbuf functions, either with rte_trace
>  > > or by other facility.
>  
>  
>  End of users Digest, Vol 466, Issue 2
>  *************************************
>