Messages in this thread | | | From | David Laight <> | Subject | RE: [net-next,v2] tcp: Improve setsockopt() TCP_USER_TIMEOUT accuracy | Date | Wed, 4 Jul 2018 14:57:06 +0000 |
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From: Neal Cardwell > Sent: 04 July 2018 15:14 > > On Tue, Jul 3, 2018 at 8:06 PM Jon Maxwell <jmaxwell37@gmail.com> wrote: > > > > Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com> > > --- > > net/ipv4/tcp_timer.c | 48 +++++++++++++++++++++++++++++++++++++++--------- > > 1 file changed, 39 insertions(+), 9 deletions(-) > > > > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c > > index 3b3611729928..d129e670d02a 100644 > > --- a/net/ipv4/tcp_timer.c > > +++ b/net/ipv4/tcp_timer.c ... > > +static __u32 tcp_clamp_rto_to_user_timeout(struct sock *sk) > > +{ > > + struct inet_connection_sock *icsk = inet_csk(sk); > > + __u32 rto = icsk->icsk_rto;
Why cache rto past all the function calls until it is needed?
> > + __u32 elapsed, user_timeout; > > + unsigned int start_ts; > > I'd suggest u32 here for start_ts (per the rationale above). > > > + > > + start_ts = tcp_retransmit_stamp(sk); > > + if (!icsk->icsk_user_timeout || !start_ts) > > + return rto; > > + elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts; > > + user_timeout = jiffies_to_msecs(icsk->icsk_user_timeout); > > + if (elapsed >= user_timeout) > > + rto = 1; /* user timeout has passed; fire ASAP */ > > + else > > + rto = min(rto, (__u32)msecs_to_jiffies(user_timeout - elapsed)); > > My sense is that min_t would be preferred here, e.g: > > rto = min_t(__u32, rto, msecs_to_jiffies(user_timeout - elapsed));
Think I'd just write the conditional...
> > + return rto; > > +}
Looks to me like it doesn't correctly allow for the conversions between millisecond and jiffies either. I suspect the msecs_to_jiffies() call can return zero (unless it rounds up). Coding with a signed 'time until user timeout' might make it simpler.
David
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