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Date: Fri, 6 May 2022 09:24:10 -0700 From: Josh Poimboeuf <jpoimboe@...nel.org> To: Artem Savkov <asavkov@...hat.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Anna-Maria Behnsen <anna-maria@...utronix.de>, "David S. Miller" <davem@...emloft.net>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v5 2/2] net: make tcp keepalive timer upper bound 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@...hat.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@...nel.org> -- Josh
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