Re: [PATCH net-next 1/3] netdev: add per-queue statistics

[Stanislav Fomichev <sdf@google.com>]

On 02/26, Jakub Kicinski wrote:
> The ethtool-nl family does a good job exposing various protocol
> related and IEEE/IETF statistics which used to get dumped under
> ethtool -S, with creative names. Queue stats don't have a netlink
> API, yet, and remain a lion's share of ethtool -S output for new
> drivers. Not only is that bad because the names differ driver to
> driver but it's also bug-prone. Intuitively drivers try to report
> only the stats for active queues, but querying ethtool stats
> involves multiple system calls, and the number of stats is
> read separately from the stats themselves. Worse still when user
> space asks for values of the stats, it doesn't inform the kernel
> how big the buffer is. If number of stats increases in the meantime
> kernel will overflow user buffer.
> 
> Add a netlink API for dumping queue stats. Queue information is
> exposed via the netdev-genl family, so add the stats there.
> Support per-queue and sum-for-device dumps. Latter will be useful
> when subsequent patches add more interesting common stats than
> just bytes and packets.
> 
> The API does not currently distinguish between HW and SW stats.
> The expectation is that the source of the stats will either not
> matter much (good packets) or be obvious (skb alloc errors).
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
>  Documentation/netlink/specs/netdev.yaml |  84 +++++++++
>  Documentation/networking/statistics.rst |  17 +-
>  include/linux/netdevice.h               |   3 +
>  include/net/netdev_queues.h             |  54 ++++++
>  include/uapi/linux/netdev.h             |  19 +++
>  net/core/netdev-genl-gen.c              |  12 ++
>  net/core/netdev-genl-gen.h              |   2 +
>  net/core/netdev-genl.c                  | 217 ++++++++++++++++++++++++
>  tools/include/uapi/linux/netdev.h       |  19 +++
>  9 files changed, 426 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> index 3addac970680..2570cc371fc8 100644
> --- a/Documentation/netlink/specs/netdev.yaml
> +++ b/Documentation/netlink/specs/netdev.yaml
> @@ -74,6 +74,10 @@ name: netdev
>      name: queue-type
>      type: enum
>      entries: [ rx, tx ]
> +  -
> +    name: stats-scope
> +    type: flags
> +    entries: [ queue ]

IIUC, in order to get netdev-scoped stats in v1 (vs rfc) is to not set
stats-scope, right? Any reason we dropped the explicit netdev entry?
It seems more robust with a separate entry and removes the ambiguity about
which stats we're querying.