Messages in this thread Patch in this message | | | From | Oleksandr Natalenko <> | Subject | [RFC] tcp_bbr2: use correct 64-bit division | Date | Mon, 23 May 2022 00:29:37 +0200 |
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Hello Neal.
It was reported to me [1] by Konstantin (in Cc) that BBRv2 code suffers from integer division issue on 32 bit systems.
Konstantin suggested a solution available in the same linked merge request and copy-pasted by me below for your convenience:
``` diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 664c9e119787..fd3f89e3a8a6 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -312,7 +312,7 @@ static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now, bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift; bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER); - segs = max_t(u32, bytes / mss_now, bbr_min_tso_segs(sk)); + segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk)); return segs; } diff --git a/net/ipv4/tcp_bbr2.c b/net/ipv4/tcp_bbr2.c index fa49e17c47ca..488429f0f3d0 100644 --- a/net/ipv4/tcp_bbr2.c +++ b/net/ipv4/tcp_bbr2.c @@ -588,7 +588,7 @@ static void bbr_debug(struct sock *sk, u32 acked, bbr_rate_kbps(sk, bbr_max_bw(sk)), /* bw: max bw */ 0ULL, /* lb: [obsolete] */ 0ULL, /* ib: [obsolete] */ - (u64)sk->sk_pacing_rate * 8 / 1000, + div_u64((u64)sk->sk_pacing_rate * 8, 1000), acked, tcp_packets_in_flight(tp), rs->is_ack_delayed ? 'd' : '.', @@ -698,7 +698,7 @@ static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now, } bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER); - segs = max_t(u32, bytes / mss_now, bbr_min_tso_segs(sk)); + segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk)); return segs; } ```
Could you please evaluate this report and check whether it is correct, and also check whether the suggested patch is acceptable? Thanks.
[1] https://gitlab.com/post-factum/pf-kernel/-/merge_requests/6
-- Oleksandr Natalenko (post-factum)
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