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Message-ID: <CANn89iJr1R4BGK2Qd+OEgsE7kEPi7X8tgyxjHnYoU7VOU_wgfA@mail.gmail.com>
Date: Thu, 6 Feb 2025 19:35:50 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Lorenzo Bianconi <lorenzo@...nel.org>, Daniel Xu <dxu@...uu.xyz>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
John Fastabend <john.fastabend@...il.com>, Toke Høiland-Jørgensen <toke@...nel.org>,
Jesper Dangaard Brouer <hawk@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, netdev@...r.kernel.org,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH net-next v4 1/8] net: gro: decouple GRO from the NAPI layer
On Thu, Feb 6, 2025 at 1:15 PM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
> Date: Wed, 5 Feb 2025 18:48:50 +0100
>
> > On Wed, Feb 5, 2025 at 5:46 PM Alexander Lobakin
> > <aleksander.lobakin@...el.com> wrote:
> >>
> >> In fact, these two are not tied closely to each other. The only
> >> requirements to GRO are to use it in the BH context and have some
> >> sane limits on the packet batches, e.g. NAPI has a limit of its
> >> budget (64/8/etc.).
> >> Move purely GRO fields into a new tagged group, &gro_node. Embed it
> >> into &napi_struct and adjust all the references. napi_id doesn't
> >> really belong to GRO, but:
> >>
> >> 1. struct gro_node has a 4-byte padding at the end anyway. If you
> >> leave napi_id outside, struct napi_struct takes additional 8 bytes
> >> (u32 napi_id + another 4-byte padding).
> >> 2. gro_receive_skb() uses it to mark skbs. We don't want to split it
> >> into two functions or add an `if`, as this would be less efficient,
> >> but we need it to be NAPI-independent. The current approach doesn't
> >> change anything for NAPI-backed GROs; for standalone ones (which
> >> are less important currently), the embedded napi_id will be just
> >> zero => no-op.
> >>
> >> Three Ethernet drivers use napi_gro_flush() not really meant to be
> >> exported, so move it to <net/gro.h> and add that include there.
> >> napi_gro_receive() is used in more than 100 drivers, keep it
> >> in <linux/netdevice.h>.
> >> This does not make GRO ready to use outside of the NAPI context
> >> yet.
> >>
> >> Tested-by: Daniel Xu <dxu@...uu.xyz>
> >> Acked-by: Jakub Kicinski <kuba@...nel.org>
> >> Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
> >> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> >> ---
> >> include/linux/netdevice.h | 26 +++++---
> >> include/net/busy_poll.h | 11 +++-
> >> include/net/gro.h | 35 +++++++----
> >> drivers/net/ethernet/brocade/bna/bnad.c | 1 +
> >> drivers/net/ethernet/cortina/gemini.c | 1 +
> >> drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c | 1 +
> >> net/core/dev.c | 60 ++++++++-----------
> >> net/core/gro.c | 69 +++++++++++-----------
> >> 8 files changed, 112 insertions(+), 92 deletions(-)
> >>
> >> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> >> index 2a59034a5fa2..d29b6ebde73f 100644
> >> --- a/include/linux/netdevice.h
> >> +++ b/include/linux/netdevice.h
> >> @@ -340,8 +340,8 @@ struct gro_list {
> >> };
> >>
> >> /*
> >> - * size of gro hash buckets, must less than bit number of
> >> - * napi_struct::gro_bitmask
> >> + * size of gro hash buckets, must be <= the number of bits in
> >> + * gro_node::bitmask
> >> */
> >> #define GRO_HASH_BUCKETS 8
> >>
> >> @@ -370,7 +370,6 @@ struct napi_struct {
> >> unsigned long state;
> >> int weight;
> >> u32 defer_hard_irqs_count;
> >> - unsigned long gro_bitmask;
> >> int (*poll)(struct napi_struct *, int);
> >> #ifdef CONFIG_NETPOLL
> >> /* CPU actively polling if netpoll is configured */
> >> @@ -379,11 +378,14 @@ struct napi_struct {
> >> /* CPU on which NAPI has been scheduled for processing */
> >> int list_owner;
> >> struct net_device *dev;
> >> - struct gro_list gro_hash[GRO_HASH_BUCKETS];
> >> struct sk_buff *skb;
> >> - struct list_head rx_list; /* Pending GRO_NORMAL skbs */
> >> - int rx_count; /* length of rx_list */
> >> - unsigned int napi_id; /* protected by netdev_lock */
> >> + struct_group_tagged(gro_node, gro,
> >> + unsigned long bitmask;
> >> + struct gro_list hash[GRO_HASH_BUCKETS];
> >> + struct list_head rx_list; /* Pending GRO_NORMAL skbs */
> >> + int rx_count; /* length of rx_list */
> >> + u32 napi_id; /* protected by netdev_lock */
> >> +
> >
> > I am old school, I would prefer a proper/standalone old C construct.
> >
> > struct gro_node {
> > unsigned long bitmask;
> > struct gro_list hash[GRO_HASH_BUCKETS];
> > struct list_head rx_list; /* Pending GRO_NORMAL skbs */
> > int rx_count; /* length of rx_list */
> > u32 napi_id; /* protected by netdev_lock */
> > };
> >
> > Really, what struct_group_tagged() can possibly bring here, other than
> > obfuscation ?
>
> You'd need to adjust every ->napi_id access, which is a lot.
> Plus, as I wrote previously, napi_id doesn't really belong here, but
> embedding it here eases life.
>
> I'm often an old school, too, but sometimes this helps a lot.
> Unless you have very strong preference on this.
>
Is struct_group_tagged even supported by ctags ?
In terms of maintenance, I am sorry to say this looks bad to me.
Even without ctags, I find git grep -n "struct xxxx {" quite good.
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