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From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [dpdk-dev] [Bug 373] i40e: TSO breaks for packets larger than 16k
Date: Mon, 02 Dec 2019 12:14:39 +0000
Message-ID: <bug-373-3@http.bugs.dpdk.org/> (raw)

https://bugs.dpdk.org/show_bug.cgi?id=373

            Bug ID: 373
           Summary: i40e: TSO breaks for packets larger than 16k
           Product: DPDK
           Version: 19.08
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: joerg.dpdk@thalheim.io
  Target Milestone: ---

According to the linux kernel the maximum buffer size per descriptor is 16k
(https://github.com/torvalds/linux/blob/596cf45cbf6e4fa7bcb0df33e373a7d062b644b5/drivers/net/ethernet/intel/i40e/i40e_txrx.h#L226).
Buffers beyond that size are distributed over multiple descriptors:
https://github.com/torvalds/linux/blob/596cf45cbf6e4fa7bcb0df33e373a7d062b644b5/drivers/net/ethernet/intel/i40e/i40e_txrx.c#L3393

DPDK however does not perform this distribution:
https://github.com/DPDK/dpdk/blob/7001c8fdb27357c67147c0a13cb3826e48c0f2bf/drivers/net/i40e/i40e_rxtx.c#L1151

This results in DPDK stop processing packets once a buffer larger 16k is
en-queued.

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