Re: Waiting for bufdaemon

From: Yasuhiro Kimura <yasu_at_utahime.org>
Subject: Re: Waiting for bufdaemon
Date: Sat, 06 Mar 2021 08:33:23 +0900 (JST)

>> My belief is that this commit helps more users than it hurts.  Namely,
>> the VMWare and KVM users, which are majority, use fast timecounter,
>> comparing to the more niche hypervisors like VirtualBox.
>> 
>> For you, a simple but manual workaround, setting the timecounter to
>> ACPI (?) or might be HPET, with a loader tunable, should do it.
> 
> Then please let me know the name of it.

From: Michael Gmelin <freebsd_at_grem.de>
Subject: Re: Waiting for bufdaemon
Date: Sat, 6 Mar 2021 00:56:43 +0100

> see `man 4 timecounters':
> 
> https://www.freebsd.org/cgi/man.cgi?query=timecounters

From: Mark Millard via freebsd-current <freebsd-current_at_freebsd.org>
Subject: Re: Waiting for bufdaemon
Date: Fri, 5 Mar 2021 17:35:14 -0800

> Its somewhat messy but there is a technique of using
> the "timecounter" in kib's wording to explore:
...

From: Chris <bsd-lists_at_bsdforge.com>
Subject: Re: Waiting for bufdaemon
Date: Fri, 05 Mar 2021 18:54:05 -0800

> Not exactly what you're asking for. But sysctl sysctl(3) and loader(8)
> will provide some good clues.

Thank you for reply.

On the system in question 'kern.timecounter.choice' and
'kern.timecounter.hardware' tunables have following values.

----------------------------------------------------------------------
yasu_at_rolling-vm-freebsd1[1002]% sysctl kern.timecounter.choice
kern.timecounter.choice: ACPI-fast(900) i8254(0) TSC-low(-100) dummy(-1000000)
yasu_at_rolling-vm-freebsd1[1003]% sysctl kern.timecounter.hardware
kern.timecounter.hardware: ACPI-fast
yasu_at_rolling-vm-freebsd1[1004]%
----------------------------------------------------------------------

So I tried setting the latter to 'i8254', 'TSC-low' and 'dummy', and
checked if the problem disappear. But unfortunately it still happened.
On the contrary changing the value from default made thing worse.
If it is set to either 'i8254' or 'TSC-low', timeout of bufdaemon also
happens when I shutdown the system just after bootstrap is completed.
And if it is set to 'dummy', the sytem hung up in the middle of
bootstrap.

So setting 'kern.timecounter.hardware' tunable doesn't work in my
case. Then is there any way to try?

---
Yasuhiro Kimura