netdev - RE: [PATCH v3 0/2] Upper bound kernel timers

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Date:   Wed, 30 Mar 2022 10:28:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Artem Savkov' <asavkov@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 0/2] Upper bound kernel timers

From: Artem Savkov
> Sent: 30 March 2022 09:21
> 
> As previously discussed [1] we had a report of a regression in TCP keepalive
> timer where timers were up to 4 minutes late resulting in disconnects.
> 
> This patchset tries to fix the problem by introducing upper bound kernel timers
> and making tcp keepalive timer use those.

Why not just fix the timer code to work properly (as it used to) so that the
timers expire within a short time of the requested interval.

This just requires that expiring 'long' timers get moved into the
higher precision 'wheels' (or whatever) before they actually expire.

The burden for this is minimal - it only affects long duration timers
that actually expire, and each timer only gets moved once for each
level of timer precision.

Perhaps you only need to move them two or three times in order to
get a reasonable accuracy.
No one is going to mind if a 5 minute timer is a second late.

	David

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