Cavium ThunderX implimentation of ODP
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README.md

ODP THUNDERX PLATFORM

RELEASE INFORMATION

This release supports ODP API version v1.11.0.0 aka Monarch LTS

PLATFORM COMPATILIBILITY

This release is compatible with following Cavium platforms:

  • ThunderX
    • CN88XX
  • Octeon TX
    • CN81XX
    • CN83XX

PACKAGE DEPENDENCIES

Platform dependencies

ODP ThunderX port has following additional dependencies:

  • Linux distributions supported (either of these):
    • Ubuntu 16.04
    • Ubuntu 16.10
  • GCC toolchain
    • ThunderX GCC toolchain. It is required for embedded rootfs and optional for Ubuntu distros
    • GCC 5.4 from Ubuntu 16.04 distribution
    • GCC 6.2 from Ubuntu 16.10 distribution
  • Linux Kernel
    • Linux 4.9.x for ThunderX
  • Kernel modules for user-space device access
    • vfio-pci, provided by kernel source (either compiled in or loaded from module)
    • kernel ThunderX VNIC PF and BGX driver, provided by kernel source (compiled in by default)

ODP build system dependencies

ODP build system requires following system tools:

  • automake
  • autoconf
  • libtool

odp-thunderx dependencies

ODP ThunderX platfrom has following dependencies:

  • OpenSSL (odp-crypto API)
  • libcunit (optional unit tests)

Building ODP ThunderX platform natively on Ubuntu 16.10 (arm64)

  1. Install dependencies:

    apt install libcunit1-dev libssl-dev

  2. Build & install using system libraries

    ./bootstrap ./configure --prefix=${INSTALL_DIR} make -j 4 make install

    Note, that installing is optional as all binaries can be used from within the project tree. Thus, --prefix option may be skipped.

Using ThunderX GCC toolchain for native compilation

  1. Download and unpack ThunderX native toolchain:

     git clone https://github.com/caviumnetworks/thunderx-tools.git
     cd thunderx-tools/thunderx-gcc_5_3-421/
     cat thunderx-gcc_* | tar xj
    
  2. Add toolchain binaries from bin/ and usr/bin/ to system path:

     export THUNDERX_TOOLS=/path/to/thunderx-gcc_5_3-421
     export PATH=${THUNDERX_TOOLS}/bin:$PATH
    
  3. Add toolchain libraries to library search path:

     export LD_LIBRARY_PATH=${THUNDERX_TOOLS}/lib64:$LD_LIBRARY_PATH
    
  4. Build otp-thunderx with --host option:

     ./bootstrap
     ./configure --host=aarch64-thunderx-linux-gnu
      make -j 4
    

BUILDING CAVIUM LINUX TREE

Download instructions

Cavium Linux tree can be downloaded from Github:

git clone https://github.com/caviumnetworks/thunderx-linux

Cross-compiling Linux Kernel for ThunderX

  1. Setup path for ThunderX toolchain as described below.

  2. Prepare cross-compilation environment for Linux

     export ARCH=arm64
     export CROSS_COMPILE=aarch64-thunderx-linux-gnu-
    
  3. Use kernel config file provided in configs/thunderx_config

     cp configs/thunderx_config .config
     make oldconfig
    
  4. Compile Linux image

     make Image -j 4
    

Compiling Linux Kernel for ThunderX on AARCH64 system

  1. Use kernel config file provided in configs/thunderx_config

     cp configs/thunderx_config .config
     make oldconfig
    
  2. Compile Linux image

     make Image -j 4
    

CROSS-COMPILING ODP FOR AARCH64

Using ThunderX GCC toolchain for cross-compilation

  1. Download and unpack ThunderX cross-toolchain:

     git clone git@github.com:caviumnetworks/thunderx-tools.git
     cd thunderx-tools/thunderx-tools-421
     cat thunderx-tools-?? | tar xj
    
  2. Add tollchain binaries from bin/ and usr/bin/ to system path:

     export THUNDERX_TOOLS=/path/to/thunderx-tools-421
     export PATH=${THUNDERX_TOOLS}/bin:${THUNDERX_TOOLS}/usr/bin:$PATH
    

Cross-compiling OpenSSL

  1. Download OpenSSL

     wget https://www.openssl.org/source/openssl-1.0.2a.tar.gz
     tar xvf openssl-1.0.2a.tar.gz
     cd openssl-1.0.2a
    
  2. Prepare cross-toolchain

      export ARCH=arm64
      export CROSS_COMPILE=aarch64-thunderx-linux-gnu-
    
  3. Build & install OpenSSL

      export OPENSSL_DIR=<choose some openssl root dir>
      ./Configure shared --openssldir=${OPENSSL_DIR} linux-aarch64
      make all install
    

Cross-compiling odp-thunderx

     cd odp-thunderx
     ./bootstrap
     ./configure --host=aarch64-thunderx-linux-gnu \
          --with-openssl-path=${OPENSSL_DIR}
     make -j 4

Cross-building ODP ThunderX platform with CUnit tests

  1. Build CUnit

      export CUNIT_DIR=<choose some cunit root dir>
      wget http://heanet.dl.sourceforge.net/project/cunit/CUnit/2.1-3/CUnit-2.1-3.tar.bz2
      tar xf CUnit-2.1-3.tar.bz2
      cd CUnit-2.1-3
      ./bootstrap
      ./configure --host=aarch64-thunderx-linux-gnu --prefix=${CUNIT_DIR}
      make all install
    
  2. Build ODP with CUnit

      ./bootstrap
      export ODP_DIR=<chose some instalation dir for ODP>
      ./configure --prefix=${ODP_DIR} \
           --host=aarch64-thunderx-linux-gnu \
           --with-openssl-path=${OPENSSL_DIR} \
           --enable-debug \
           --enable-cunit-support \
           --with-cunit-path=${CUNIT_DIR}
      make all install
    

BULDING OPTIONS

There are 4 environment variables controlling compilation options:

  • ODP_CFLAGS_EXTRA - for compilation options, e.g. defines, includes
  • LIBS - for additional libraries, e.g. -ldl
  • LDFLAGS - for linker flags, e.g. -pie
  • EXTRA_CFLAGS - dynamic compilation options that could be added to make process

Additinally, configure cript presents another option for performance-oriented builds:

  • --enable-lto enables Link Time Optimization if toolchain can support it

They can be used along with "configure" script, eg.:

   ./configure --prefix=${ODP_DIR} \
        --host=aarch64-thunderx-linux-gnu \
        --with-openssl-path=${OPENSSL_DIR} \
        --disable-debug-print \
        ODP_CFLAGS_EXTRA="-O3 -g" \
        LIBS="-ldl"

There are 2 options controlling debug level:

  • "--enable-debug-print", "--disable-debug-print" - controls ODP internal debug messages, disabled by default. It is recommended to disable this option, as such verbose logging is useful only for debugging the ODP platform.
  • "--enable-debug", "--disable-debug" - controls ODP internal debug assertions, disable by default. This option improves error diagnostics at the expense of slightly lower performance (c.a. 5%).

For highest speed, the recommended build options are:

  • Cavium tollchain (either cross or native)
  • all debug options turned off (dafault)
  • --enable-lto

E.g Simplest option is native build with Cavium tollchain:

     ./configure --prefix=${ODP_DIR} \
          --host=aarch64-thunderx-linux-gnu \
          --enable-lto

It is measured that link time optimization improves performance of ODP platform by 10% due to aggressive inter-modular in-lining. However, this option degrades debugging experience as most function symbols disappear, so "-flto" option is useful only for release builds or performance evaluation.

If you are intrested in ODP test suite, please use following options durring configure stage: --enable-test-perf --enable-test-vald

Additional compilation options for ODP platform behavior

There are several ODP ThunderX port defines which influence on compilation:

  • NIC_QUEUE_STATS – adding of -DNIC_QUEUE_STATS to ODP_CFLAGS_EXTRA allow application to print out the internal NIC statistics to console. For that additional odp_pktio_stats_dump() ODP API function was added to ThunderX port. Using of this option may slightly decrease performance.

  • ODP_DISABLE_CLASSIFICATION and NIC_DISABLE_PACKET_PARSING – if user application does not use classification subsystem, adding of -DODP_DISABLE_CLASSIFICATION and -DNIC_DISABLE_PACKET_PARSING to ODP_CFLAGS_EXTRA will increase the performance. This is because ThunderX does not have any HW assisted classification and this process need to be done for every packet received purely by SW. Direct usage of pktio interface is not affected. Classification is done only when packet are received by using odp_schedule() or any of odp_queue_enq/deq() functions.

ThunderX SYSTEM SETUP

Below you may find requirements and actions which need to be meet before you start your ODP applications.

  • Cunit shared library in rootfs (in case of running unit tests and proper configure)
  • vfio, thunder-nicpf and BGX modules loaded to kernel (typically no driver needs to be loaded since all mentioned modules are compiled into kernel image)
  • Hugetlbfs must be mounted with considerable amount of pages added to it (min 256MB of memory) ODP ThunderX uses huge pages for maximize performance by eliminating TLB misses. Especially for few HW related cases physically contiguous memory is needed. Therefore ODP ThunderX memory allocator tries to allocate contiguous memory area. In the case ODP application startup problems increasing the hugepage pool is recommended (by adding more pages to the pool than required).
  • NIC VFs need to be bound to VFIO framework

Detail of those can be found below:

Hugetlbfs

     mkdir -p /dev/huge
     mount -t hugetlbfs none /dev/huge
     echo 256 > /proc/sys/vm/nr_hugepages

If you see problems with ODP application startup due inefficient amount continuous memory pages, increase the number of pages from 256 to 512.

The number of huge memory pages required for application is dependent on interface count and thread count. Each interface requires RBDR_SIZE buffers, which currently is 16k buffers each of ~2k. Keep in mind that buffer size is application dependent. Each thread requires additionally ODP_CONFIG_POOL_CACHE_SIZE buffers to fill up its buffer pool cache, currently is 4k buffers. Summarizing with 8 interfaces and 16 threads the memory requirements are as follows: 8 * 16k = 131072 buffers for RBDR fillup 16 * 4k = 65536 buffers for thread buffer cache sum = 196608 buffer each 2k size = 384MB of memory = 192 huge pages of 2M size on top of that we have to add all the buffers which application may process (in flight buffers). All of mentioned sizes are configurable by user (mentioned defines). Example application uses two defines to calculate the size of the buffer pools POOL_SIZE_GLOBAL and POOL_SIZE_THREAD.

Opening Pktio, naming convention for interfaces

odp_packetio_open() accepts following string patterns as interface names.

  vfio:group-1.group-2.group-n

The above naming convention means that:

  • with single VF (specified by single vfio group), odp_pktio_open() can open up to 8 HW queues on the same interface.
  • it is possible to open more than 8 HW queues on the same interface. To do that VF's need to be combined. It means user must supply more than single vfio group by using mentioned string pattern as interface name
  • Because of kernel driver limitations, not all VF's can be combined together. Depending on physical interfaces, some number of first VF's are always the primary VF's. All remain ones are secondary VF's. In combined VF there has to be exacly one primary and one or more secondary VF's.

Examples:

Using single VF (iommu group 59) with 8 queues, the odp_pktio_open() string will be like the following:

odp_pktio_t pktio = odp_pktio_open("vfio:59", ...)

Using combined VF's (iommu groups 59, 82) with 16 queues, the odp_pktio_open() string will be like the following:

odp_pktio_t pktio = odp_pktio_open("vfio:59.82", ...)

How to get the vfio VF numbers is described in following sections. As mentioned, there is kernel limitation on which VF's can be combined together. Put attention to this fact while reading below section.

Using multiple VFs per interface

There are two types of VFs:

  • Primary VF
  • Secondary VF

Each port consists of a primary VF and n secondary VF(s). Each VF provides 8 Tx/Rx queues to a port. When a given port is configured to use more than 8 queues, it requires one (or more) secondary VF. Each secondary VF adds 8 additional queues to the queue set.

During PMD driver initialization, the primary VF’s are enumerated by checking the specific flag. They are at the beginning of VF list (the remain ones are secondary VF’s).

The primary VFs are used as master queue sets. Secondary VFs provide additional queue sets for primary ones. If a port is configured for more then 8 queues than it will request for additional queues from secondary VFs.

Secondary VFs cannot be shared between primary VFs.

Primary VFs are present on the beginning of the ‘Network devices using kernel driver’ list, secondary VFs are on the remaining on the remaining part of the list. As a rule, each VF that is not by default bound by Linux to network device is a secondary VF.

Binding NIC interfaces

Userspace dataplane application need to access VF interface either by VFIO driver. Interfaces can be binded to VFIO-PCI driver by following procedure:

     echo 0002:01:00.2 > /sys/bus/pci/devices/0002\:01\:00.2/driver/unbind

     modprobe vfio-pci #if not compiled in the kernel

     echo 177d 0011 > /sys/bus/pci/drivers/vfio-pci/new_id
     VFIO_GROUP=$(readlink /sys/bus/pci/devices/0002\:01\:00.2/iommu_group)

ODP platform top-level directory also contains "bind.sh" script which can be used for reference and also as a handy tool which automates those steps. The script can be used as follows:

     ./bind.sh --help
    Usage:
      bind.sh <DEVICE> <DRIVER>
    where:
    <DEVICE> [[[<domain>:]<bus>:]<slot>].<func>
    examples:
    Bind function 1 of the first matching device, e.g. 0002:01:00.1 to vfio-pci
      bind.sh 1 vfio-pci
    Bind device 01:00.2 of the first matching domain, e.g. 0002:01:00.2 to vfio-pci
      bind.sh 01:00.2 vfio-pci

Called without parameters it shows:

  • which NVIC virtual function is bound to which driver
  • does it have netdev name (e.g. eth0) in case of kernel-controlled device
  • iommu group of the device, useful for VFIO backend

Example:

./bind.sh
0002:01:00.1 thunder-nicvf eth0 iommu group 36
0002:01:00.2 vfio-pci iommu group 37
0002:01:00.3 vfio-pci iommu group 38
0002:01:00.4 thunder-nicvf iommu group 39
0002:01:00.5 thunder-nicvf iommu group 40
0002:01:00.6 thunder-nicvf iommu group 41
0002:01:00.7 thunder-nicvf iommu group 42
0002:01:01.0 thunder-nicvf iommu group 43

Called with VF PCI device number and driver, binds the VF device to the appropriate framework:

./bind.sh 5 vfio-pci
Binding 0002:01:00.5 to vfio-pci...
0002:01:00.5 vfio-pci
vfio group 38

Binding to "thunder-nicvf" brings back the device under kernel control:

./bind.sh 5 thunder-nicvf
Binding 0002:01:00.5 to thunder-nicvf...
0002:01:00.5 thunder-nicvf

PCI device numbering works as follows:

  • Single number means device function number, rest of the number is the from the first match of the device list, e.g. for device list:

     0002:01:00.1 thunder-nicvf eth0 iommu group 36
     0002:01:00.2 vfio-pci iommu group 37
     0002:01:02.0 thunder-nicvf iommu group 51
     0002:01:02.1 thunder-nicvf iommu group 52
     0002:01:02.2 thunder-nicvf iommu group 53
    

    number 2 means 0002:01:00.2 (appears before 0002:01:02.2). This scheme is useful as by default all ethernet ports occupy 0002:01:00 device which is always first.

  • device.function works the same as above but only domain and bus is looked up on list.

  • An unambiguous way to specify device is bus:device.function and domain:bus:device.function

Bellow example shows how to prepare VF's to driver binding for utilization of more than 8 queues per VF (also named as combined VF's).

./bind.sh
0002:01:00.1 thunder-nicvf eth4 iommu group 59
0002:01:00.2 thunder-nicvf eth1 iommu group 60
0002:01:00.3 thunder-nicvf eth2 iommu group 61
0002:01:00.4 thunder-nicvf eth3 iommu group 62
0002:01:00.5 thunder-nicvf eth0 iommu group 63
0002:01:00.6 thunder-nicvf iommu group 64
0002:01:00.7 thunder-nicvf iommu group 65
0002:01:01.0 thunder-nicvf iommu group 66
0002:01:01.1 thunder-nicvf iommu group 67
0002:01:01.2 thunder-nicvf iommu group 68
0002:01:01.3 thunder-nicvf iommu group 69
0002:01:01.4 thunder-nicvf iommu group 70

When you first run the ./bind.sh script, you will see that some of the VF's are assigned to kernel thunder-nicvf driver and have linux eth name assigned. Those VF's are the primary ones. The remaining ones are secondary VF's. Depending on number of physical interfaces your configuration may differ from the mentioned example.

For combined VF, you need exactly one primary and at least one secondary VF. Therefore in mentioned example, if you would like to bind 0002:01:00.1 with some secondary VF, the first which you can use is 0002:01:00.6. In case of vfio, after bind operation you should get following state

./bind.sh
0002:01:00.1 vfio-pci iommu group 59
0002:01:00.2 thunder-nicvf eth1 iommu group 60
0002:01:00.3 thunder-nicvf eth2 iommu group 61
0002:01:00.4 thunder-nicvf eth3 iommu group 62
0002:01:00.5 thunder-nicvf eth0 iommu group 63
0002:01:00.6 vfio-pci iommu group 64
0002:01:00.7 thunder-nicvf iommu group 65
0002:01:01.0 thunder-nicvf iommu group 66
0002:01:01.1 thunder-nicvf iommu group 67
0002:01:01.2 thunder-nicvf iommu group 68
0002:01:01.3 thunder-nicvf iommu group 69

You can now use vfio group 59 and 64 for combined VF.

USAGE EXAMPLES

ODP platform has 2 example applications, which can be used out of the box for ODP ThunderX evaluation:

  • l2fwd - simple l2 forwarding
  • pktgen - traffic sniffer and generator

To get help:

     ./test/performance/odp_l2fwd
     ./example/pktgen/pktgen

We do not recommend use of examples/generator/odp_generator as it is not well implemented and obsolete.

pktgen

Passive receive using VFIO group 30

     ./example/pktgen/pktgen -i vfio:30 -m r

Generating traffic using VFIO group 59

     ./example/pktgen/pktgen -I vfio:59 --srcmac 02:01:01:01:01:01 --dstmac 02:01:01:01:01:02 --srcip 192.168.0.1 --dstip 192.168.0.2 -s 0 -m s -n 11

l2fwd

Echoing packets to the same port with 2 cores:

     ./test/performance/l2fwd/odp_l2fwd -i vfio:30 -m 0 -c 2

Forwarding packets between two ports bound to vfio:30 and vfio:31 with 2 cores

     ./test/performance/l2fwd/odp_l2fwd -i vfio:30,vfio:31 -m 0 -c 2

Forwarding packets between queues on single pktio interface (loopback) bound to compined VF's with 16 queues (iommu groups 59, 64) using 16 cores (one worker per queue):

     ./test/performance/l2fwd/odp_l2fwd -i vfio:59.64 -c 16 -m 0

ARCHITECTURE NOTES

ThunderX VNIC driver for Linux

ThunderX VNIC driver is implemented in two parts: Physical function (PF) and Virtual Functions (VF). This driver can be found at drivers/net/ethernet/cavium/thunder/ in kernel tree.

PF coordinates VNIC global handling and it is designed "supervisor" for VFs. Therefore PF is implemented as kernel driver so it can act with highest access rights.

VF is a part of driver assigned to virtual function of NIC and can be either implemented by kernel driver or by user-space driver. In ThunderX ODP port this is done in user-space code linked with ODP application (see odp/platform/linux-thunder/nic_*.c files).

Because VF and PF need to cooperate they need to use the same definitions of common structures. Current ThunderX ODP port is supported by kernel code which is from SDK release v2.0.

Because ODP application need direct access to NIC device, it needs proper kernel driver which allows that kind of access. This can be done either by uio or vfio modules.

ODP ThunderX platform software architecture

ODP ThunderX port has following naming convention for source files:

  • low-level VNIC driver (nic_*.c files)
  • higher-level ODP layers (odp_*.c)

ODP ThunderX port was based on linux-generic, customized to meet the platform requirements and optimized for performance.

Low-level VNIC driver

The driver is a series of functions operating on ThunderX VNIC hardware resources. This driver has following areas of integration with ODP and platform layers:

  • packet data structure

    • shared with ODP and higher layers
  • PCI device attachment, e.g mapping BARs

    • VFIO framework, no exposure to higher layers
  • physical memory allocator - odp_shared_memory.c

    • provides physically and virtually contiguous memory regions
    • provides physical addresses for allocated regions
    • intended for global allocations done only once
    • no need for high performance implementation
    • used at the beginning of ODP startup
    • used by odp_pktio_open to allocate all necessary memory regions
  • packet memory allocator - odp_buffer_pool.c

    • allocates memory from physical allocator
    • keeps packets in SMP-safe memory pool
    • converts between virtual and physical addresses
  • malloc-like allocator for various data structures

    • reused physical allocator

Physical memory allocator

Userspace programs do not have access do physical memory by standard means, however:

  • Hugetlbfs provides physically contiguous pages of size at 2MB or 512MB on ARMv8 (depending on page size 4k/64k).

  • Linux has /proc//pagemap interface that returns physical address of a page.

  • Huge pages can be re-mapped to form virtually and physically contiguous region as long as the system can provide enough physically adjacent huge pages.

Implementation notes:

  • Is it recommended to allocate a hugepage pool that is 50% bigger than required memory consumption. That reduces the risk of memory fragmentation.

  • There is no hard guarantee that system will provide enough physically adjacent huge pages. In case of memory issues, the memory pool can be simply increased or pre-allocated at boot time. Rerer to ./Documentation/vm/hugetlbpage.txt in the kernel sources.

  • The huge pool is used for all ODP objects including buffer pools. Buffer pool is asosiated with pktio and it is used for allocating buffers for RX and TX.

  • Therefore in order to avoid potential problems with non symmetrical usage of pktio TX and RX paths, the buffer pool size need to be declared (allocated) as bigger than sum of all internal pktio queues multiplied by number of pktios opened on the same interface. Each pktio is using one RBDR, SQ and RQ queue (look for SND_QUEUE_LEN, RCV_BUF_COUNT and odp_pool_create()).

Packet pool

Packet is a chain of buffers of constant size. Each buffer should be big enough to store:

  • whole MTU (1500 B)
  • metadata, currently 128 B
  • additional headroom at the beginning, if required, configured to 128 B

Packets received from HW can form chains if:

  • S/W is using Jumbo frames from time to time but tries to save memory
  • S/W is using TCP offloads provided by ThunderX VNIC. Currently not supported.
  • It is recommended to adjuct the basic buffer size if Jumbo frames are to be used frequently, e.g. for frequent use of 4K frames it is best to have single 4K buffer instead of a chain.

Packet memory should be aligned to cache line size, which is 128 B on Thunder-88x, so 128B is a minimal memory occupation for packet metadata. Headroom can be 0.

Memory pool consists of:

  • global multi-producer - multi-consumer buffer ring
  • thread-local cache implemented as table (stack) of 4096 entries

This implementation provides high-performance, low-overhead packet management but consumes more memory than linux-generic counterpart, because there is no guarantee that cached packets return to global pool. The pool operates optimally when allocations are done in bulk, since it amortizes memory barrier costs for global pool.

Packet IO implementation notes

Packet IO is optimized for bulk transmit/receive. For highest performance it is recommended to process packets in batches of 32 or 64. Packet can be received/sent by two access methods provided by ODP API:

  • Raw pktio method (optimized for DIRECT pktio mode)
    • odp_pktout_send and odp_pktin_recv, both were optimized with ODP_PKTOUT_MODE_DIRECT and ODP_PKTOUT_MODE_DIRECT respectively
    • thread-safe access to H/W queues
    • packet parsing done by H/W, i.e L3/L4 recognition
    • the lowest possible overhead method of getting/xmiting packets
    • requires more effort while designing the application (packet ordering and thread/queue binding).
  • Queued/Scheduled method (not optimized)
    • odp_schedule() or direct queue operations odp_queue_deq/enq()
    • operate with scheduler & classifier and the rest of ODP API
    • slower than raw method due to classifier & queue overhead
    • allows easier application design while using many threads for processing
    • ordering is guaranteed by queue type while using odp_schedule()

Caveats

  1. VNIC hardware should be always reset at application exit to keep the system stable.

    H/W reset is done in odp_pktio_close(), so software should always call it before termination. Moreover, the application should strive to provide an exit handler for most common signals, e.g. SIGTERM, SIGINT. The odp_l2fwd.c example file contains such handler for reference.

    Sudden application crash leaving H/W in undefined state may cause issues with subsequent launching the app. In that case, several retries should bring the H/W back.

  2. Sudden application exit may lead to random-writer scenario and can crash subsequent application launches or other software.

    When the application suddenly crashes, e.g. by SIGSEGV, odp_pktio_close() is not called and VNIC H/W still receives packets and writes to memory until it runs out of buffers. Since VNIC hardware operates on physical memory, the pages used for packet reception can be overwritten even when they return to kernel and get allocated again. The best way to avoid it is to re-launch the application, which triggers H/W reset. Installing signal handler is the best prevention method.