Re: [PATCH v5 0/2] Upper bound kernel timers

Josh Poimboeuf
2022-07-26T22:42:18Z

Hi Thomas,

Ping?

On Thu, May 05, 2022 at 03:18:09PM +0200, Artem Savkov wrote:
> 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.
>
> [1] https://lore.kernel.org/all/20210302001054.4qgrvnkltvkgikzr@treble/T/#u
>
> ---
> Changes in v5:
> - The least intrusive and most straightforward approach. This avoids touching
> any of existing code. The timeout supplied is always reduced by a known
> timer wheel error margin of 12.5%.
> - Commit message adjustments.
>
> Changes in v4:
> - Drop any attempts to be smart when calculating timer adjustment and always
> substract LVL_GRAN so that base clock lag won't be such a problem. This
> means that in some cases we will always be early, but all we want is not to
> be late.
>
> Changes in v3:
> - A different approach: instead of introducing upper bound timers try to
> account for timer wheen granularity on timer (re)arming step.
> - Not sure whether moving lvl calculation into a separate function is worth
> it.
> - Had a hard time naming the upper_bount_timeout() function - any suggestions
> welcome.
>
> Changes in v2:
> - TIMER_UPPER_BOUND flag description added as a comment in timer.h
> - Code style fixes
> - More elaborate commit message in timer commit
>
> Artem Savkov (2):
> timer: add a function to adjust timeouts to be upper bound
> net: make tcp keepalive timer upper bound
>
> include/linux/timer.h | 1 +
> kernel/time/timer.c | 14 ++++++++++++++
> net/ipv4/inet_connection_sock.c | 2 +-
> 3 files changed, 16 insertions(+), 1 deletion(-)
>
> --
> 2.34.1
>

--
Josh