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Message-ID: <Zd0EJq3gS2_p9NQ8@google.com>
Date: Mon, 26 Feb 2024 13:35:34 -0800
From: Stanislav Fomichev <sdf@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
pabeni@...hat.com, amritha.nambiar@...el.com, danielj@...dia.com,
mst@...hat.com, michael.chan@...adcom.com, vadim.fedorenko@...ux.dev
Subject: Re: [PATCH net-next 1/3] netdev: add per-queue statistics
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@...nel.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.
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