[Vm-dev] Re: [Pharo-dev] Reducing the activity of the image

Tue Feb 10 18:34:57 UTC 2015

It's a bit more complicated and what platform you are on does matter. Just
hunt in the squeak mailing list 10 years back for getNextWakeupTick

Possibly the mac vm still calls getNextWakeupTick() which returns the next
time the VM has to wake up to service a delay pop.
Normally that is less than 1/50 of a second out due to the Morphic polling
cycle, say 16 - 20 milliseconds.

The idea I had was to sleep until the VM needs to wakeup since when
the ioRelinquishProcessorForMicroseconds
is made we know we can sleep and the VM knows exactly when the next time to
wake up is. Unfortunately we have to deal with user interrupts (i/o sockets
ui)

Some platforms might use nanosleep() (#if defined(HAVE_NANOSLEEP)) which
might wake when a socket interrupt arrives, but I've never confirmed that.
Anyway off then to call aioPoll() where the bulk of the cpu is consumed. I
note that obviously avoiding calling aioPoll() will affect socket
performance of course.
http://www.squeakvm.org/svn/squeak/branches/Cog/platforms/unix/vm/aio.c

I note you can't properly calculate next wakeup tick in smalltalk code due
to the rather brittle code base in the Delay logic. Attempts I made a
decade back always resulted in a deadlock situation, which is why that
calculation is done in the VM. I had last taken a serious look at this back
in 2010 and found very strange oddities such as calling
ioRelinquishProcessorForMicroseconds
yet a wakeup time is now, or in the past.. Obviously one needed to explore
the stack traces to understand why no process was runnable, yet a process
was scheduled to be woken...

Anyway compare ioRelinquishProcessorForMicroseconds
http://www.squeakvm.org/svn/squeak/branches/Cog/platforms/iOS/vm/Common/Classes/sqMacV2Time.c

Against whatever is being compiled for your target platform VM and what
exactly HAVE_NANOSLEEP is when the VM is compiled.
Also check idle CPU usage for say a OS X Squeak 4.2.5 VM against I'm assume
a unix vm flavor as you can run both on the same os-x machine for
comparison using the same image/etc.

On Tue, Feb 10, 2015 at 3:03 AM, Norbert Hartl <norbert at hartl.name> wrote:

>
> Am 10.02.2015 um 11:23 schrieb Sven Van Caekenberghe <sven at stfx.eu>:
>
>
> On 10 Feb 2015, at 11:19, Norbert Hartl <norbert at hartl.name> wrote:
>
> Sven,
>
> Am 10.02.2015 um 10:36 schrieb Sven Van Caekenberghe <sven at stfx.eu>:
>
>
> On 10 Feb 2015, at 09:51, Norbert Hartl <norbert at hartl.name> wrote:
>
>
> Am 10.02.2015 um 09:23 schrieb Clément Bera <bera.clement at gmail.com>:
>
> Hello,
>
> About the Morphic rendering loop, the delay between rendering is handled
> in WorldState>>#interCyclePause:. The best solution to reduce the cost of
> the Morphic rendering loop is to put it in server mode by executing in
> Pharo: WorldState serverMode: true. In squeak you have to set that in the
> Preferences.
>
> I'll play with it and see what can be gained.
>
>
> I tried the following on an otherwise idle DigitalOcean VM running Ubuntu
> 13.10
>
> $ mkdir pharo4
> $ curl get.pharo.org/40+vm | bash
> $ ./pharo Pharo.image save Server
>
> First patch (slower event handling, extra delay of 50ms):
>
> $ ./pharo Server.image eval --save 'WorldState serverMode: true'
>
> Second patch (give time back to OS while idle for 10ms instead of for 1ms):
>
> $ cat ProcessorScheduler-class-idleProcess.st
> 'From Pharo4.0 of 18 March 2013 [Latest update: #40484] on 10 February
> 2015 at 9:49:15.412839 am!ProcessorScheduler class methodsFor: 'background
> process' stamp: 'SvenVanCaekenberghe 2/10/2015idleProc[true] w[self
> relinquishProcessorForMicroseconds: 10000]! !
>
> $ ./pharo Server.image eval "'ProcessorScheduler-class-idleProcess.st'
> asFileReference fileIn"
> $ ./pharo Server.image eval '(ProcessorScheduler class>>#idleProcess)
> sourceCode'
> 'idleProcess
> "A default background process which is invisible."
>
> [true] whileTrue:
>  [self relinquishProcessorForMicroseconds: 10000]'
>
> Run an image with a basic Zn HTTP server in background:
>
> $ ./pharo Server.image eval --no-quit 'ZnServer startDefaultOn: 1701' &
> $ curl http://localhost:1701
>
> Overall load is 0.01% but this is virtual/shared hardware, so who knows.
>
> CPU load of the pharo process hovers around a couple of %, I am not seeing
> much difference, maybe it is a bit lower, but that might be wishful
> thinking.
>
> my findings are similar. I have a CPU usage of 6%. WorldState serverMode
> adds a Delay for 50ms. Setting a higher number in the idle process does not
> seem to have any effect until the number is too high, then the image does
> not start anymore.
> I tuned all of these things and it is not faster sometimes it appears to
> take more CPU which probably is not true.
>
>
> I am afraid that we as a community do not fully understand what is
> happening or how we can control it.
>
> On the other hand, on a machine with many images running, things are still
> totally fine, so we should not worry too much. It is only in specific case
> like yours where it becomes a concern.
>
> I can say that
>
> pharo-vm-nox --noevents --nohandlers  --notimer --headless -vm-sound-null
> /opt/nted/image/NTed.image --no-quit eval "RFBServer stop; reset. ZnServer
> managedServers do: #stop. UIManager default uiProcess suspend. WorldState
> serverMode: true. ProcessorScheduler class compile: 'idleProcess',String
> cr,'[true] whileTrue: [self relinquishProcessorForMicroseconds: 10000]'.
> ProcessorScheduler startUp"
>
> does not make a difference at all. My assumption here is to switch
> everything off, don't use sockets, try to sleep as much as possible.
> But....nothing.
>
> Norbert
>
>
> But as it was discussed, the cpu consumption most probably does not come
> from Morphic but comes from the idle loop, which can be solved by doing an
> event-driven VM.
>
> I am particularly willing to have an event-driven VM because it then means
> that the VM performance would then be directly proportional to the cpu
> consumption. For example, theoretically, with an event-driven VM, having
> the VM twice faster with Spur would also mean that the VM consumes twice
> less energy. Go Green IT :-)
>
> That is exactly my point. While consumed energy is turned into heat the
> act of saving energy is the same as having a cool device (pun intended).
>
> So I would like to take my consortium hat to state my upvote on this.
>
> Norbert
>
> 2015-02-10 8:00 GMT+01:00 Eliot Miranda <eliot.miranda at gmail.com>:
>
>
>
> On Feb 9, 2015, at 10:41 PM, Sven Van Caekenberghe <sven at stfx.eu> wrote:
>
>
> On 10 Feb 2015, at 01:55, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
> Hi Sven,
>
> On Mon, Feb 9, 2015 at 1:43 PM, Sven Van Caekenberghe <sven at stfx.eu>
> wrote:
> There is some timer thread between the image and the vm that ticks every
> millisecond, that is the cause. I don't know what it does but it is
> apparently needed.
>
> Anyway, that is how I understood it from Igor and Eliot, long ago.
>
> So basically, the VM is always slightly busy.
>
> Yet the VM is always slightly busy with the heartbeat thread, but this is
> very cheap.  The actual idle cost comes form the idle loop in the
> background process that sends relinquishProcessorForMicroseconds:, which is
> a primitive that eventually calls the select system call.  This is the
> source of the cost.
>
>
> Can we change something about that ?
> Maybe just as an experiment to prove your point ?
>
>
> What do you think halving or doubling the argument to
> relinquishProcessorForMicroseconds: should do if this is the major source
> of overhead?  Processor usage at idle should be closely inversely
> proportional right?
>
>
> On 09 Feb 2015, at 21:11, Norbert Hartl <norbert at hartl.name> wrote:
>
> I have an installation where a pharo powered hardware is used in a closed
> case. Over time that collects quite some heat. One reason for this is that
> the pharo vm is taking approx. 6% CPU all the time. The only thing that
> happens is network/sockets. I suspended the ui thread in the image but on
> this platform it doesn't help.
> Are there any tweaks to lower the polling and the activity of the image/vm
> even more?
>
> thanks,
>
> Norbert
>
> --
> best,
> Eliot
>
>
>

-- 
===========================================================================
John M. McIntosh <johnmci at smalltalkconsulting.com>
https://www.linkedin.com/in/smalltalk
===========================================================================
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.squeakfoundation.org/pipermail/vm-dev/attachments/20150210/6207c64a/attachment-0001.htm