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Message-ID: <CAL+tcoBi=0OzxmoGk56V4OSzJ+u3BD+Nfx8p3MTXGUwU69Kiaw@mail.gmail.com> Date: Fri, 11 Aug 2023 10:35:27 +0800 From: Jason Xing <kerneljasonxing@...il.com> To: Simon Horman <horms@...nel.org> Cc: edumazet@...gle.com, davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, pabeni@...hat.com, apetlund@...ula.no, netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com> Subject: Re: [PATCH net] net: fix the RTO timer retransmitting skb every 1ms if linear option is enabled On Fri, Aug 11, 2023 at 4:32 AM Simon Horman <horms@...nel.org> wrote: > > On Thu, Aug 10, 2023 at 07:21:48PM +0800, Jason Xing wrote: > > From: Jason Xing <kernelxing@...cent.com> > > > > In the real workload, I encountered an issue which could cause the RTO > > timer to retransmit the skb per 1ms with linear option enabled. The amount > > of lost-retransmitted skbs can go up to 1000+ instantly. > > > > The root cause is that if the icsk_rto happens to be zero in the 6th round > > (which is the TCP_THIN_LINEAR_RETRIES value), then it will alway be zero > > nit: alway -> always > > checkpatch.pl --codespell is your friend Thanks for your reminder. > > > due to the changed calculation method in tcp_retransmit_timer() as follows: > > > > icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); > > > > Above line could be converted to > > icsk->icsk_rto = min(0 << 1, TCP_RTO_MAX) = 0 > > > > Therefore, the timer expires so quickly without any doubt. > > > > I read through the RFC 6298 and found that the RTO value can be rounded > > up to a certain value, in Linux, say TCP_RTO_MIN as default, which is > > regarded as the lower bound in this patch as suggested by Eric. > > > > Fixes: 36e31b0af587 ("net: TCP thin linear timeouts") > > Suggested-by: Eric Dumazet <edumazet@...gle.com> > > Signed-off-by: Jason Xing <kernelxing@...cent.com> > > --- > > net/ipv4/tcp_timer.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c > > index d45c96c7f5a4..b2b25861355c 100644 > > --- a/net/ipv4/tcp_timer.c > > +++ b/net/ipv4/tcp_timer.c > > @@ -599,7 +599,9 @@ void tcp_retransmit_timer(struct sock *sk) > > tcp_stream_is_thin(tp) && > > icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { > > icsk->icsk_backoff = 0; > > - icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); > > + icsk->icsk_rto = clamp(__tcp_set_rto(tp), > > + tcp_rto_min(sk), > > + TCP_RTO_MAX); > > nit: this indentation looks a bit odd. Yeah, I'm always stuck with this kind of indentation issue. I'll fix it in v2 patch. Thanks, Jason > > icsk->icsk_rto = clamp(__tcp_set_rto(tp), > tcp_rto_min(sk), > TCP_RTO_MAX); > > > } else if (sk->sk_state != TCP_SYN_SENT || > > icsk->icsk_backoff > > > READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) { > > -- > > 2.37.3 > > > >
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