[Simh] DECwindows issues

Tue Jul 24 00:27:50 EDT 2018

Hi Hans,

Notice:      “Time taken by msleep(1): 20ms”

Well, the simulator framework implements idling with sleeps.  Meanwhile the simulated VAX has a clock which is architecturally defined to tick at 10ms intervals.  If any call to sleep for 1 millisecond actually sleeps for 20 milliseconds, then whenever the system idles the clock is going to get far behind.  Older simh versions would simply refuse to idle when the sleep granularity was too large.  The current implementation tries to actually allow idling when the host system’s sleep is large and also tries hard to schedule catchup clock ticks so that simulated time tracks pretty closely with wall clock time.

This attempt to run with catchup clock ticks, hasn’t been extensively tested since only a few BSD systems actually have large scheduling clock ticks built into the kernel by default.  Therefore, there may be problems.  Most other systems (Windows, Linux, and OS X) have host system clock ticks on the order of 1-2ms so these systems don’t have this problem.
You can build a kernel for your BSD system by specifying or changing the value of HZ somewhere in the kernel configuration information, or you could try running on a different host platform.

-          Mark
From: Hans Hübner [mailto:hans.huebner at gmail.com]
Sent: Friday, July 20, 2018 10:57 PM
To: Mark Pizzolato <Mark at infocomm.com>
Cc: Matt Burke <matt at 9track.net>; Simh <simh at trailing-edge.com>
Subject: Re: [Simh] DECwindows issues

Hi Matt,

2018-07-20 20:26 GMT-04:00 Mark Pizzolato <Mark at infocomm.com<mailto:Mark at infocomm.com>>:
On Friday, July 20, 2018 3:45 PM, Hans Hübner  wrote:
> 2018-07-20 18:28 GMT-04:00 Matt Burke <matt at 9track.net<mailto:matt at 9track.net>>:
> > On 19/07/2018 06:41, Hans Hübner wrote:
> > > I see either one of the DECwindows processes (window or session
> > > manager) use more than 50% of the VAX CPU or, if I kill both
> > > processes, the emulator taking up 100% of its host CPU with no VAX
> > > process showing up in MONITOR PROC/TOPCPU.  The emulated system is too
> > > slow to be used, effectively.
> >
> > I don't seem to be able to reproduce this (on Debian 9.5).
>
> I'm running SIMH on FreeBSD, but I can switch if the problem is related to that.

It might be related to the host OS.

Please let it get to the state you're complaining about and then:
^E
sim> SHOW VERSION
sim> CLOCK
sim> SHOW CPU

and send the output produced back here.

Here you go:

sim> show version
VAXStation 3900 (KA655) simulator V4.0-0 Current
    Simulator Framework Capabilities:
        64b data
        64b addresses
        Threaded Ethernet Packet transports:PCAP:TAP:NAT:UDP
        Idle/Throttling support is available
        Virtual Hard Disk (VHD) support
        Asynchronous I/O support (Lock free asynchronous event queue)
        Asynchronous Clock support
        FrontPanel API Version 12
    Host Platform:
        Compiler: GCC 6.4.0
        Simulator Compiled as C arch: x64 (Release Build) on Jul 18 2018 at 07:32:15
        Memory Access: Little Endian
        Memory Pointer Size: 64 bits
        Large File (>2GB) support
        SDL Video support: SDL Version 2.0.7
        PCRE RegEx (Version 8.42 2018-03-20) support for EXPECT commands
        OS clock resolution: 1ms
        Time taken by msleep(1): 20ms
        OS: FreeBSD vaxhost 11.2-RELEASE FreeBSD 11.2-RELEASE #0 r335510: Fri Jun 22 04:32:14 UTC 2018     root at releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC<mailto:root at releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC>  amd64
        git commit id: 15fd71b9
        git commit time: 2018-07-17T22:05:05-0700
sim> show clock
Minimum Host Sleep Time:       20 ms (50Hz)
Host Clock Resolution:         1 ms
Execution Rate:                1,358,783,530 cycles/sec
Idling:                        Enabled
Time before Idling starts:     20 seconds
Calibrated Timer:              Internal Timer
Catchup Ticks:                 Enabled for clocks ticking faster than 50 Hz
Calibration:                   Always

VAXStation 3900 (KA655) clock device is CLK
Calibrated Timer 0:
  Running at:                100 Hz
  Tick Size:                 10 msecs
  Ticks in current second:   82
  Seconds Running:           80 (1:20 minutes)
  Real Time:                 3144059812
  Virtual Time:              3144059812
  Next Interval:             1,000
  Base Tick Delay:           5,000
  Initial Insts Per Tick:    5,000
  Current Insts Per Tick:    13,587,835
  Initializations:           5
  Ticks:                     6,795
  Total Ticks:               8,082
  Peak Clock Skew:           825.867 msecs slow
  Ticks Acked:               6,795
  Tick Time:                 1:07.95 minutes
  Total Tick Time:           1:20.81 minutes
  Catchup Ticks Sched:       6,065
  Initialize Base Time:      07:53:37.188
  Tick Start Time:           07:53:37.196
  Wall Clock Time Now:       07:55:35.790
  Catchup Tick Time:         07:54:56.606
  Catchup Base Time:         07:53:48.656
  Total Time Idled:          2.439 seconds
VAXStation 3900 (KA655) clock device is Internal Calibrated Timer(INT-TIMER)
Calibrated Timer 8:
  Running at:                10 Hz
  Tick Size:                 100 msecs
  Ticks in current second:   6
  Seconds Running:           23 (23 seconds)
  Calibration Opportunities: 23
  Instruction Time:          1570864774
  Real Time:                 3144081177
  Virtual Time:              3144082804
  Next Interval:             1,500
  Base Tick Delay:           90,585,569
  Initial Insts Per Tick:    50,000
  Current Insts Per Tick:    135,878,353
  Initializations:           3
  Ticks:                     235
  Tick Time:                 23.5 seconds
  Initialize Base Time:      07:53:37.180
  Tick Start Time:           07:53:37.180
  Wall Clock Time Now:       07:55:35.790
sim> show cpu
CPU  idle=VMS, idle enabled, model=MicroVAX 3900 (KA655), NOAUTOBOOT
          64MB, HALT to SIMH

Thanks!
Hans
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.trailing-edge.com/pipermail/simh/attachments/20180723/41e2202c/attachment-0001.html>