Re: [PATCH v5 2/2] net: make tcp keepalive timer upper bound

Josh Poimboeuf
2022-05-06T16:24:17Z

On Fri, May 06, 2022 at 08:39:08AM +0200, Artem Savkov wrote:
> On Thu, May 05, 2022 at 10:56:54AM -0700, Josh Poimboeuf wrote:
> > On Thu, May 05, 2022 at 03:18:11PM +0200, Artem Savkov wrote:
> > > Make sure TCP keepalive timer does not expire late. Switching to upper
> > > bound timers means it can fire off early but in case of keepalive
> > > tcp_keepalive_timer() handler checks elapsed time and resets the timer
> > > if it was triggered early. This results in timer "cascading" to a
> > > higher precision and being just a couple of milliseconds off it's
> > > original mark.
> > > This adds minimal overhead as keepalive timers are never re-armed and
> > > are usually quite long.
> > >
> > > Signed-off-by: Artem Savkov <asavkov@redhat.com>
> > > ---
> > > net/ipv4/inet_connection_sock.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > > index 1e5b53c2bb26..bb2dbfb6f5b5 100644
> > > --- a/net/ipv4/inet_connection_sock.c
> > > +++ b/net/ipv4/inet_connection_sock.c
> > > @@ -589,7 +589,7 @@ EXPORT_SYMBOL(inet_csk_delete_keepalive_timer);
> > >
> > > void inet_csk_reset_keepalive_timer(struct sock *sk, unsigned long len)
> > > {
> > > - sk_reset_timer(sk, &sk->sk_timer, jiffies + len);
> > > + sk_reset_timer(sk, &sk->sk_timer, jiffies + upper_bound_timeout(len));
> > > }
> > > EXPORT_SYMBOL(inet_csk_reset_keepalive_timer);
> >
> > As I mentioned before, there might be two sides to the same coin,
> > depending on whether the keepalive is detecting vs preventing the
> > disconnect. So this might possibly fix one case, while breaking
> > another.
>
> But cascading is still there in the handler so it will fire off quite
> close to original timer in any case.

Ah, indeed it does. Sorry, I should try actually reading the patch
description next time :-/ Looks good to me.

Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>

--
Josh