Re: misc/57300: Time system is not accurate on NetBSD VM

[Nan Xiao <nan%chinadtrace.org@localhost>]

The following reply was made to PR misc/57300; it has been noted by GNATS.

From: Nan Xiao <nan%chinadtrace.org@localhost>
To: gnats-bugs%netbsd.org@localhost, misc-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Cc: 
Subject: Re: misc/57300: Time system is not accurate on NetBSD VM
Date: Mon, 27 Mar 2023 17:28:03 +0800

 Hi Michael,
 
 Thanks very much for your reply! "clockinterrupt" seems working for my
 VM environment.
 
 
 On 2023/3/26 6:50 PM, Michael van Elst wrote:
 > The following reply was made to PR misc/57300; it has been noted by GNATS.
 > 
 > From: mlelstv%serpens.de@localhost (Michael van Elst)
 > To: gnats-bugs%netbsd.org@localhost
 > Cc: 
 > Subject: Re: misc/57300: Time system is not accurate on NetBSD VM
 > Date: Sun, 26 Mar 2023 10:44:17 -0000 (UTC)
 > 
 >  nan%chinadtrace.org@localhost writes:
 >  
 >  >-bash-5.1$ date; sleep 10; date
 >  >Sun Mar 26 18:59:44 +08 2023
 >  >Sun Mar 26 19:00:13 +08 2023
 >  
 >  >Actually the time just passes 10 seconds, but date command shows it has passes nearly half a minute. Not sure whether this could be accounted as NetBSD bug, or VirtualBox bug, thanks!
 >  
 >  
 >  "sleep 10" waits 1000 clock interrupts. If that lasts 10 seconds, the
 >  emulation of clock interrupts is correct. The exact delay can vary
 >  with host speed and load.
 >  
 >  "date" looks at the current timecounter. If that advances 30 seconds
 >  in 10 seconds, the emulation of the timecounter is bad. Fortunately we
 >  have multiple, e.g.:
 >  
 >  # sysctl kern.timecounter
 >  kern.timecounter.choice = TSC(q=3000, f=3292677360 Hz) clockinterrupt(q=0, f=100 Hz) ichlpcib0(q=1000, f=3579545 Hz) hpet0(q=2000, f=14318180 Hz) ACPI-Fast(q=1000, f=3579545 Hz) lapic(q=-100, f=99859155 Hz) i8254(q=100, f=1193182 Hz) dummy(q=-1000000, f=1000000 Hz)
 >  kern.timecounter.hardware = TSC
 >  kern.timecounter.timestepwarnings = 0
 >  
 >  By setting kern.timecounter.hardware to one of the choices you may get
 >  a timecounter that works better.
 >  
 >  While the choice "clockinterrupt" avoids discrepancies between "sleep"
 >  and "date", the result might not be accurate. For many cases a different
 >  choice (if there is any) is better.
 >  
 >  
 
 -- 
 Best Regards
 Nan Xiao(è??æ¥ )