Subject: Re: [PATCH net-next v2 2/4] selftests: drv-net: add helper to wait for HW stats to sync

From: Petr Machata <[email-masked]>
Date: Tue, 25 Jun 2024 12:04:24 +0200

Jakub Kicinski <[email-masked]> writes:

> Some devices DMA stats to the host periodically. Add a helper
> which can wait for that to happen, based on frequency reported
> by the driver in ethtool.
>
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
> v2:
>  - sleep for 25ms on top of the driver DMA period
>    (and remove confusing comment)
> ---
>  .../selftests/drivers/net/lib/py/env.py       | 20 ++++++++++++++++++-
>  tools/testing/selftests/net/lib/py/utils.py   |  4 ++++
>  2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/drivers/net/lib/py/env.py b/tools/testing/selftests/drivers/net/lib/py/env.py
> index edcedd7bffab..16d24fe7107d 100644
> --- a/tools/testing/selftests/drivers/net/lib/py/env.py
> +++ b/tools/testing/selftests/drivers/net/lib/py/env.py
> @@ -1,9 +1,10 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  import os
> +import time
>  from pathlib import Path
>  from lib.py import KsftSkipEx, KsftXfailEx
> -from lib.py import cmd, ip
> +from lib.py import cmd, ethtool, ip
>  from lib.py import NetNS, NetdevSimDev
>  from .remote import Remote
>  
> @@ -82,6 +83,8 @@ from .remote import Remote
>  
>          self.env = _load_env_file(src_path)
>  
> +        self._stats_settle_time = None
> +
>          # Things we try to destroy
>          self.remote = None
>          # These are for local testing state
> @@ -222,3 +225,18 @@ from .remote import Remote
>          if remote:
>              if not self._require_cmd(comm, "remote"):
>                  raise KsftSkipEx("Test requires (remote) command: " + comm)
> +
> +    def wait_hw_stats_settle(self):
> +        """
> +        Wait for HW stats to become consistent, some devices DMA HW stats
> +        periodically so events won't be reflected until next sync.
> +        Good drivers will tell us via ethtool what their sync period is.
> +        """
> +        if self._stats_settle_time is None:
> +            self._stats_settle_time = 0.025
> +
> +            data = ethtool("-c " + self.ifname, json=True)[0]
> +            if 'stats-block-usecs' in data:
> +                self._stats_settle_time += data['stats-block-usecs'] / 1000 / 1000

If there's a v3, this dual check-then-access could be folded into a
.get() and the whole expression then gets a bit simpler:

            data = ethtool("-c " + self.ifname, json=True)[0]
            self._stats_settle_time = 0.25 + \
                    data.get('stats-block-usecs', 0) / 1000 / 1000

> +
> +        time.sleep(self._stats_settle_time)
> diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
> index 16907b51e034..11dbdd3b7612 100644
> --- a/tools/testing/selftests/net/lib/py/utils.py
> +++ b/tools/testing/selftests/net/lib/py/utils.py
> @@ -78,6 +78,10 @@ import time
>      return tool('ip', args, json=json, host=host)
>  
>  
> +def ethtool(args, json=None, ns=None, host=None):
> +    return tool('ethtool', args,  json=json, ns=ns, host=host)

Double space here.

> +
> +
>  def rand_port():
>      """
>      Get a random unprivileged port, try to make sure it's not already used.