From: "Emil Tsalapatis" <emil@etsalapatis.com>
To: <chia-yu.chang@nokia-bell-labs.com>, <jolsa@kernel.org>,
<yonghong.song@linux.dev>, <song@kernel.org>,
<linux-kselftest@vger.kernel.org>, <memxor@gmail.com>,
<shuah@kernel.org>, <martin.lau@linux.dev>, <ast@kernel.org>,
<daniel@iogearbox.net>, <andrii@kernel.org>, <eddyz87@gmail.com>,
<horms@kernel.org>, <dsahern@kernel.org>, <bpf@vger.kernel.org>,
<netdev@vger.kernel.org>, <pabeni@redhat.com>, <jhs@mojatatu.com>,
<kuba@kernel.org>, <stephen@networkplumber.org>,
<davem@davemloft.net>, <edumazet@google.com>,
<andrew+netdev@lunn.ch>, <donald.hunter@gmail.com>,
<kuniyu@google.com>, <ij@kernel.org>, <ncardwell@google.com>,
<koen.de_schepper@nokia-bell-labs.com>, <g.white@cablelabs.com>,
<ingemar.s.johansson@ericsson.com>,
<mirja.kuehlewind@ericsson.com>, <cheshire@apple.com>,
<rs.ietf@gmx.at>, <Jason_Livingood@comcast.com>,
<vidhi_goel@apple.com>
Subject: Re: [PATCH v3 net-next 1/1] tcp: Replace min_tso_segs() with tso_segs() CC callback
Date: Mon, 27 Jul 2026 19:32:42 -0400 [thread overview]
Message-ID: <DK9QVC2YO30L.3TKTHLE7TXS0D@etsalapatis.com> (raw)
In-Reply-To: <20260630120145.286497-1-chia-yu.chang@nokia-bell-labs.com>
On Tue Jun 30, 2026 at 8:01 AM EDT, chia-yu.chang wrote:
> From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
>
> This patch replaces existing min_tso_segs() with tso_segs() CC callbak
> for CC algorithm to provides explicit tso segment number of each data
> burst and overrides tcp_tso_autosize().
>
> This change provides below impacts on BPF struct_ops users:
> - The callback is renamed from min_tso_segs to tso_segs
> - The signature gains an extra u32 mss_now argument
> - The return value semantics is changed from "floor value passed into
> tcp_tso_autosize()" to "final tso_segs value", bypassing autosizing
>
> As a result, BPF programs shall be updated, beccause retuning a small
> constans will now directly limit tso_segs instead of the minimum.
>
> Signed-off-by: Ilpo Järvinen <ij@kernel.org>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
As mentioned in v4, from a BPF standpoint this is cleaner. Feel free to
add:
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
> ---
> include/net/tcp.h | 13 +++++++++++--
> net/ipv4/bpf_tcp_ca.c | 8 +++++---
> net/ipv4/tcp_bbr.c | 13 ++++++++++---
> net/ipv4/tcp_output.c | 13 +++++++------
> tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c | 8 ++++----
> 5 files changed, 37 insertions(+), 18 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 6d376ea4d1c0..7fb42a0ce7da 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -824,6 +824,9 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
> unsigned int tcp_current_mss(struct sock *sk);
> u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when);
>
> +u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
> + int min_tso_segs);
> +
> /* Bound MSS / TSO packet size with the half of the window */
> static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
> {
> @@ -1361,8 +1364,14 @@ struct tcp_congestion_ops {
> /* hook for packet ack accounting (optional) */
> void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
>
> - /* override sysctl_tcp_min_tso_segs (optional) */
> - u32 (*min_tso_segs)(struct sock *sk);
> + /*
> + * Override tcp_tso_autosize (optional)
> + *
> + * If provided, this callback returns the final TSO segment number
> + * and will bypass tcp_tso_autosize() entirely. The implementation
> + * must derive an appropriate value and ensure the result is valid.
> + */
> + u32 (*tso_segs)(struct sock *sk, u32 mss_now);
>
> /* new value of cwnd after loss (required) */
> u32 (*undo_cwnd)(struct sock *sk);
> diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
> index 791e15063237..27c4cdfd80a8 100644
> --- a/net/ipv4/bpf_tcp_ca.c
> +++ b/net/ipv4/bpf_tcp_ca.c
> @@ -284,9 +284,11 @@ static void bpf_tcp_ca_pkts_acked(struct sock *sk, const struct ack_sample *samp
> {
> }
>
> -static u32 bpf_tcp_ca_min_tso_segs(struct sock *sk)
> +static u32 bpf_tcp_ca_tso_segs(struct sock *sk, u32 mss_now)
> {
> - return 0;
> + if (unlikely(!mss_now))
> + return U32_MAX;
> + return tcp_tso_autosize(sk, mss_now, 0);
> }
>
> static void bpf_tcp_ca_cong_control(struct sock *sk, u32 ack, int flag,
> @@ -320,7 +322,7 @@ static struct tcp_congestion_ops __bpf_ops_tcp_congestion_ops = {
> .cwnd_event_tx_start = bpf_tcp_ca_cwnd_event_tx_start,
> .in_ack_event = bpf_tcp_ca_in_ack_event,
> .pkts_acked = bpf_tcp_ca_pkts_acked,
> - .min_tso_segs = bpf_tcp_ca_min_tso_segs,
> + .tso_segs = bpf_tcp_ca_tso_segs,
> .cong_control = bpf_tcp_ca_cong_control,
> .undo_cwnd = bpf_tcp_ca_undo_cwnd,
> .sndbuf_expand = bpf_tcp_ca_sndbuf_expand,
> diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
> index 82378a2bfd1e..b63e77b14c65 100644
> --- a/net/ipv4/tcp_bbr.c
> +++ b/net/ipv4/tcp_bbr.c
> @@ -297,11 +297,18 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
> }
>
> /* override sysctl_tcp_min_tso_segs */
> -__bpf_kfunc static u32 bbr_min_tso_segs(struct sock *sk)
> +static u32 bbr_min_tso_segs(struct sock *sk)
> {
> return READ_ONCE(sk->sk_pacing_rate) < (bbr_min_tso_rate >> 3) ? 1 : 2;
> }
>
> +__bpf_kfunc static u32 bbr_tso_segs(struct sock *sk, u32 mss_now)
> +{
> + if (unlikely(!mss_now))
> + return U32_MAX;
> + return tcp_tso_autosize(sk, mss_now, bbr_min_tso_segs(sk));
> +}
> +
> static u32 bbr_tso_segs_goal(struct sock *sk)
> {
> struct tcp_sock *tp = tcp_sk(sk);
> @@ -1151,7 +1158,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
> .undo_cwnd = bbr_undo_cwnd,
> .cwnd_event_tx_start = bbr_cwnd_event_tx_start,
> .ssthresh = bbr_ssthresh,
> - .min_tso_segs = bbr_min_tso_segs,
> + .tso_segs = bbr_tso_segs,
> .get_info = bbr_get_info,
> .set_state = bbr_set_state,
> };
> @@ -1163,7 +1170,7 @@ BTF_ID_FLAGS(func, bbr_sndbuf_expand)
> BTF_ID_FLAGS(func, bbr_undo_cwnd)
> BTF_ID_FLAGS(func, bbr_cwnd_event_tx_start)
> BTF_ID_FLAGS(func, bbr_ssthresh)
> -BTF_ID_FLAGS(func, bbr_min_tso_segs)
> +BTF_ID_FLAGS(func, bbr_tso_segs)
> BTF_ID_FLAGS(func, bbr_set_state)
> BTF_KFUNCS_END(tcp_bbr_check_kfunc_ids)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 00ec4b5900f2..f3fc4b64e61d 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2253,8 +2253,8 @@ static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
> * for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance
> * is below 1500 bytes after 6 * ~500 usec = 3ms.
> */
> -static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
> - int min_tso_segs)
> +u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
> + int min_tso_segs)
> {
> unsigned long bytes;
> u32 r;
> @@ -2269,6 +2269,7 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
>
> return max_t(u32, bytes / mss_now, min_tso_segs);
> }
> +EXPORT_SYMBOL(tcp_tso_autosize);
>
> /* Return the number of segments we want in the skb we are transmitting.
> * See if congestion control module wants to decide; otherwise, autosize.
> @@ -2278,11 +2279,11 @@ static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
> const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
> u32 min_tso, tso_segs;
>
> - min_tso = ca_ops->min_tso_segs ?
> - ca_ops->min_tso_segs(sk) :
> - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
> + min_tso = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
>
> - tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
> + tso_segs = ca_ops->tso_segs ?
> + ca_ops->tso_segs(sk, mss_now) :
> + tcp_tso_autosize(sk, mss_now, min_tso);
> return min_t(u32, tso_segs, sk->sk_gso_max_segs);
> }
>
> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c b/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c
> index 0a3e9d35bf6f..58262e490336 100644
> --- a/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c
> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c
> @@ -10,7 +10,7 @@ extern u32 bbr_sndbuf_expand(struct sock *sk) __ksym;
> extern u32 bbr_undo_cwnd(struct sock *sk) __ksym;
> extern void bbr_cwnd_event_tx_start(struct sock *sk) __ksym;
> extern u32 bbr_ssthresh(struct sock *sk) __ksym;
> -extern u32 bbr_min_tso_segs(struct sock *sk) __ksym;
> +extern u32 bbr_tso_segs(struct sock *sk, u32 mss_now) __ksym;
> extern void bbr_set_state(struct sock *sk, u8 new_state) __ksym;
>
> extern void dctcp_init(struct sock *sk) __ksym;
> @@ -90,9 +90,9 @@ u32 BPF_PROG(ssthresh, struct sock *sk)
> }
>
> SEC("struct_ops")
> -u32 BPF_PROG(min_tso_segs, struct sock *sk)
> +u32 BPF_PROG(tso_segs, struct sock *sk, u32 mss_now)
> {
> - return bbr_min_tso_segs(sk);
> + return bbr_tso_segs(sk, mss_now);
> }
>
> SEC("struct_ops")
> @@ -120,7 +120,7 @@ struct tcp_congestion_ops tcp_ca_kfunc = {
> .cwnd_event = (void *)cwnd_event,
> .cwnd_event_tx_start = (void *)cwnd_event_tx_start,
> .ssthresh = (void *)ssthresh,
> - .min_tso_segs = (void *)min_tso_segs,
> + .tso_segs = (void *)tso_segs,
> .set_state = (void *)set_state,
> .pkts_acked = (void *)pkts_acked,
> .name = "tcp_ca_kfunc",
prev parent reply other threads:[~2026-07-27 23:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-30 12:01 [PATCH v3 net-next 1/1] tcp: Replace min_tso_segs() with tso_segs() CC callback chia-yu.chang
2026-06-30 23:20 ` Alexei Starovoitov
2026-07-01 5:46 ` Chia-Yu Chang (Nokia)
2026-07-01 5:56 ` Alexei Starovoitov
2026-07-01 16:16 ` Koen De Schepper (Nokia)
2026-07-09 12:06 ` Chia-Yu Chang (Nokia)
2026-07-27 23:32 ` Emil Tsalapatis [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=DK9QVC2YO30L.3TKTHLE7TXS0D@etsalapatis.com \
--to=emil@etsalapatis.com \
--cc=Jason_Livingood@comcast.com \
--cc=andrew+netdev@lunn.ch \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=cheshire@apple.com \
--cc=chia-yu.chang@nokia-bell-labs.com \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=donald.hunter@gmail.com \
--cc=dsahern@kernel.org \
--cc=eddyz87@gmail.com \
--cc=edumazet@google.com \
--cc=g.white@cablelabs.com \
--cc=horms@kernel.org \
--cc=ij@kernel.org \
--cc=ingemar.s.johansson@ericsson.com \
--cc=jhs@mojatatu.com \
--cc=jolsa@kernel.org \
--cc=koen.de_schepper@nokia-bell-labs.com \
--cc=kuba@kernel.org \
--cc=kuniyu@google.com \
--cc=linux-kselftest@vger.kernel.org \
--cc=martin.lau@linux.dev \
--cc=memxor@gmail.com \
--cc=mirja.kuehlewind@ericsson.com \
--cc=ncardwell@google.com \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=rs.ietf@gmx.at \
--cc=shuah@kernel.org \
--cc=song@kernel.org \
--cc=stephen@networkplumber.org \
--cc=vidhi_goel@apple.com \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox