[Bug 256217] [tcp] High system load because of interrupts with RACK

From: <bugzilla-noreply_at_freebsd.org>
Date: Sat, 29 May 2021 11:45:15 UTC

--- Comment #9 from Christos Chatzaras <chris@cretaforce.gr> ---
HPTS system is "kern.eventtimer.timer=HPET", right? With HPET I see (with
"top") ~ 2 times more interrupts in comparison with LAPIC.

I tried again to reproduce the issue with a STABLE/13 kernel and it exists too.
Next I will try with a CURRENT kernel as I see some fixes for RACK.

Regarding the "stuck" connection in LAST_ACK state someone tries to brute force
SSH and "sshguard" blocks the connections (I have 4 "stuck" connection for SSH
at the moment). Also I have 2 "stuck" connections in port 80 from "wrk
benchmark". I found this:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=25986 which is old PR but
@johalun replied that he can see this issue few months ago. But they are not
talking about "rack" so this is not related. The only relation with "rack" is
that these "stuck" connections create interrupts. At the moment these
connections "stuck" for more than 35 minutes. Also I see some "stuck"
connections in other servers that use "freebsd" stack.

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