Re: Waiting for bufdaemon

Dear src committers,

From: Yasuhiro Kimura <yasu_at_utahime.org>
Subject: Re: Waiting for bufdaemon
Date: Thu, 28 Jan 2021 05:02:42 +0900 (JST)

>>> I have been experiencing same problem with my 13-CURRENT amd64
>>> VirtualBox VM for about a month. The conditions that the problem
>>> happens are unclear and all what I can say is
>>> 
>>> * It happens only after I login in the VM and do something for a
>>>   while. If I boot the VM and shut it down immediately, it never
>>>   happens.
>>> * When the problem happens, one or more unkillable processes seem to
>>>   be left.
>> 
>> CPU of my host is not AMD but Intel. According to the
>> /var/run/dmesg.boot of VM, information of CPU is as following.
>> 
>> CPU: Intel(R) Core(TM) i7-9700 CPU _at_ 3.00GHz (3000.09-MHz K8-class CPU)
>>   Origin="GenuineIntel"  Id=0x906ed  Family=0x6  Model=0x9e  Stepping=13
>>   Features=0x1783fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE,SSE2,HTT>
>>   Features2=0x5eda2203<SSE3,PCLMULQDQ,SSSE3,CX16,PCID,SSE4.1,SSE4.2,MOVBE,POPCNT,AESNI,XSAVE,OSXSAVE,AVX,RDRAND>
>>   AMD Features=0x28100800<SYSCALL,NX,RDTSCP,LM>
>>   AMD Features2=0x121<LAHF,ABM,Prefetch>
>>   Structured Extended Features=0x842421<FSGSBASE,AVX2,INVPCID,NFPUSG,RDSEED,CLFLUSHOPT>
>>   Structured Extended Features3=0x30000400<MD_CLEAR,L1DFL,ARCH_CAP>
>>   IA32_ARCH_CAPS=0x29<RDCL_NO,SKIP_L1DFL_VME,MDS_NO>
>>   TSC: P-state invariant
>> 
>> Just FYI.
> 
> It took for a while to investigate, but according to the result of
> bisect following commit is the source of problem in my case.
> 
> ----------------------------------------------------------------------
> commit 84eaf2ccc6a
> Author: Konstantin Belousov <kib_at_FreeBSD.org>
> Date:   Mon Dec 21 19:02:31 2020 +0200
> 
>     x86: stop punishing VMs with low priority for TSC timecounter
>     
>     I suspect that virtualization techniques improved from the time when we
>     have to effectively disable TSC use in VM.  For instance, it was reported
>     (complained) in https://github.com/JuliaLang/julia/issues/38877 that
>     FreeBSD is groundlessly slow on AWS with some loads.
>     
>     Remove the check and start watching for complaints.
>     
>     Reviewed by:    emaste, grehan
>     Discussed with: cperciva
>     Sponsored by:   The FreeBSD Foundation
>     Differential Revision:  https://reviews.freebsd.org/D27629
> ----------------------------------------------------------------------
> 
> I confirmed the problem still happens with 5c325977b11 but reverting
> above commit fixes it.

Would someone please revert above commit from main, stable/13 and
releng/13.0? As I wrote previous mail I submitted this problem to
Bugzilla as bug 253087 and added the committer to Cc. But there is no
response for 34 days.

I confirmed the problem still happens with 37cd6c20dbc of main and
13.0-RC1.

Best Regards.

---
Yasuhiro Kimura