> net: mark skb NAPI IDs independently of busy polling
TL;DR: Commit message only: it blames e68b6e50fa35 for gating skb NAPI IDs on
busy polling, but that gating predates it; 97dc7cd92ac6 introduced the
dependency. Suggests rewording.
> net: mark skb NAPI IDs independently of busy polling
>
> Commit 97dc7cd92ac6 ("ptp: Support late timestamp determination")
> added support for deferring RX timestamp conversion to
> ndo_get_tstamp(). When the timestamp is consumed, get_timestamp()
> uses the skb's NAPI ID to find the device that owns the timestamp
> cookie and invoke its callback.
> Commit e68b6e50fa35 ("udp: enable busy polling for all sockets")
> gated NAPI ID bookkeeping with CONFIG_NET_RX_BUSY_POLL. As a result,
> when busy polling is disabled, the skb may not carry a usable NAPI ID.
> The device lookup then fails, so the driver callback is not invoked.
> get_timestamp() falls back to hwtstamp, which does not contain the
> converted timestamp, resulting in an incorrect RX hardware timestamp.
> Record skb NAPI IDs independently of busy-poll support to support
> drivers that use deferred timestamp conversion and future driver
> features that need to look up a device by its NAPI ID.
> Signed-off-by: Ding Meng <[email protected]>
> Reviewed-by: Florian Bezdeka <[email protected]>
This isn't a bug, but is e68b6e50fa35 the right commit to name here?
Before that commit, __skb_mark_napi_id() / skb_mark_napi_id() was already
inside '#ifdef CONFIG_NET_RX_BUSY_POLL' with an empty stub in the #else
branch, and struct sk_buff already had napi_id under
'#if defined(CONFIG_NET_RX_BUSY_POLL) || defined(CONFIG_XPS)'. That gating
goes back to 8b80cda536ea ("net: rename ll methods to busy-poll").
e68b6e50fa35 only moved the socket-side sk_mark_napi_id() out of the ifdef
block and added sk_mark_napi_id_once(). Both act on sk->sk_napi_id, not on
the skb.
It is also about six years older than 97dc7cd92ac6, so the message reads as
if a later change broke the deferred-timestamp lookup. In fact
get_timestamp() has depended on a busy-poll-only skb field (skb_napi_id()
returns 0 when CONFIG_NET_RX_BUSY_POLL=n) since 97dc7cd92ac6 added it.
Could the message say that the skb NAPI ID was always busy-poll-only and
that 97dc7cd92ac6 started depending on it?
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