testing: net-drv: use stats64 for testing

JIRA: https://issues.redhat.com/browse/RHEL-57764

commit a61a459
Author: Joe Damato <jdamato@fastly.com>
Date:   Mon May 20 23:58:43 2024 +0000

    testing: net-drv: use stats64 for testing

    Testing a network device that has large numbers of bytes/packets may
    overflow. Using stats64 when comparing fixes this problem.

    I tripped on this while iterating on a qstats patch for mlx5. See below
    for confirmation without my added code that this is a bug.

    Before this patch (with added debugging output):

    $ NETIF=eth0 tools/testing/selftests/drivers/net/stats.py
    KTAP version 1
    1..4
    ok 1 stats.check_pause
    ok 2 stats.check_fec
    rstat: 481708634 qstat: 666201639514 key: tx-bytes
    not ok 3 stats.pkt_byte_sum
    ok 4 stats.qstat_by_ifindex

    Note the huge delta above ^^^ in the rtnl vs qstats.

    After this patch:

    $ NETIF=eth0 tools/testing/selftests/drivers/net/stats.py
    KTAP version 1
    1..4
    ok 1 stats.check_pause
    ok 2 stats.check_fec
    ok 3 stats.pkt_byte_sum
    ok 4 stats.qstat_by_ifindex

    It looks like rtnl_fill_stats in net/core/rtnetlink.c will attempt to
    copy the 64bit stats into a 32bit structure which is probably why this
    behavior is occurring.

    To show this is happening, you can get the underlying stats that the
    stats.py test uses like this:

    $ ./cli.py --spec ../../../Documentation/netlink/specs/rt_link.yaml \
               --do getlink --json '{"ifi-index": 7}'

    And examine the output (heavily snipped to show relevant fields):

     'stats': {
               'multicast': 3739197,
               'rx-bytes': 1201525399,
               'rx-packets': 56807158,
               'tx-bytes': 492404458,
               'tx-packets': 1200285371,

     'stats64': {
                 'multicast': 3739197,
                 'rx-bytes': 35561263767,
                 'rx-packets': 56807158,
                 'tx-bytes': 666212335338,
                 'tx-packets': 1200285371,

    The stats.py test prior to this patch was using the 'stats' structure
    above, which matches the failure output on my system.

    Comparing side by side, rx-bytes and tx-bytes, and getting ethtool -S
    output:

    rx-bytes stats:    1201525399
    rx-bytes stats64: 35561263767
    rx-bytes ethtool: 36203402638

    tx-bytes stats:      492404458
    tx-bytes stats64: 666212335338
    tx-bytes ethtool: 666215360113

    Note that the above was taken from a system with an mlx5 NIC, which only
    exposes ndo_get_stats64.

    Based on the ethtool output and qstat output, it appears that stats.py
    should be updated to use the 'stats64' structure for accurate
    comparisons when packet/byte counters get very large.

    To confirm that this was not related to the qstats code I was iterating
    on, I booted a kernel without my driver changes and re-ran the test
    which shows the qstats are skipped (as they don't exist for mlx5):

    NETIF=eth0 tools/testing/selftests/drivers/net/stats.py
    KTAP version 1
    1..4
    ok 1 stats.check_pause
    ok 2 stats.check_fec
    ok 3 stats.pkt_byte_sum # SKIP qstats not supported by the device
    ok 4 stats.qstat_by_ifindex # SKIP No ifindex supports qstats

    But, fetching the stats using the CLI

    $ ./cli.py --spec ../../../Documentation/netlink/specs/rt_link.yaml \
               --do getlink --json '{"ifi-index": 7}'

    Shows the same issue (heavily snipped for relevant fields only):

     'stats': {
               'multicast': 105489,
               'rx-bytes': 530879526,
               'rx-packets': 751415,
               'tx-bytes': 2510191396,
               'tx-packets': 27700323,
     'stats64': {
                 'multicast': 105489,
                 'rx-bytes': 530879526,
                 'rx-packets': 751415,
                 'tx-bytes': 15395093284,
                 'tx-packets': 27700323,

    Comparing side by side with ethtool -S on the unmodified mlx5 driver:

    tx-bytes stats:    2510191396
    tx-bytes stats64: 15395093284
    tx-bytes ethtool: 17718435810

    Fixes: f0e6c86 ("testing: net-drv: add a driver test for stats reporting")
    Signed-off-by: Joe Damato <jdamato@fastly.com>
    Link: https://lore.kernel.org/r/20240520235850.190041-1-jdamato@fastly.com
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: Ivan Vecera <ivecera@redhat.com>

Author: ivecera

tools/testing/selftests/drivers/net/stats.py

@@ -69,7 +69,7 @@ def stat_cmp(rstat, qstat):
         return 0
 
     for _ in range(10):
-        rtstat = rtnl.getlink({"ifi-index": cfg.ifindex})['stats']
+        rtstat = rtnl.getlink({"ifi-index": cfg.ifindex})['stats64']
         if stat_cmp(rtstat, qstat) < 0:
             raise Exception("RTNL stats are lower, fetched later")
         qstat = get_qstat(cfg)