From: David Laight <David.Laight@ACULAB.COM>
To: 'Josh Poimboeuf' <jpoimboe@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Artem Savkov <asavkov@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Anna-Maria Behnsen <anna-maria@linutronix.de>
Subject: RE: Upper bound mode for kernel timers
Date: Wed, 3 Mar 2021 14:06:03 +0000 [thread overview]
Message-ID: <5efd5c6a00dc46529767c428a81ec9e0@AcuMS.aculab.com> (raw)
In-Reply-To: <20210302001054.4qgrvnkltvkgikzr@treble>
From: Josh Poimboeuf
> Sent: 02 March 2021 00:11
>
> We had a report of a regression in the TCP keepalive timer. The user
> had a 3600s keepalive timer for preventing firewall disconnects (on a
> 3650s interval). They observed keepalive timers coming in up to four
> minutes late, causing unexpected disconnects.
>
> The regression was observed to have come from the timer wheel rewrite
> from almost five years ago:
>
> 500462a9de65 ("timers: Switch to a non-cascading wheel")
>
> As you mentioned, with a HZ of 1000, the granularity for a one-hour
> timer is four minutes, which matches the seen behavior.
That seems horribly broken - if technically valid.
Reading the big comment even the 32sec for the next finer 'wheel'
seems a little coarse for a 1h timer.
The second finer wheel has 4sec resolution - which is probably reasonable.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2021-03-03 18:11 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 0:10 Josh Poimboeuf
2021-03-03 14:06 ` David Laight [this message]
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