[Vm-dev] Heartbeat & Linux

Mon Apr 22 17:31:09 UTC 2013

On 2013-04-22, at 19:16, Eliot Miranda <eliot.miranda at gmail.com> wrote:

> 
> 
> On Mon, Apr 22, 2013 at 5:33 AM, Bert Freudenberg <bert at freudenbergs.de> wrote:
>  
> Still, you make it sound like this inefficiency is actually preventing the Stack VM from running on the Raspberry Pi? That is hard to believe.
> 
> No, we just use the interval timer.  But as I say in a server/multi-user/ffi context the interval timer is problematic.

Okay. So for the typical local single pi user it should be fine :) 

Btw, what kind of deadlocks have you seen with SA_RESTART? Normally that should avoid the EINTR problems.

- Bert -

> 
> - Bert -
> 
> On 2013-04-19, at 05:24, Casey Ransberger <casey.obrien.r at gmail.com> wrote:
> 
>> I had a feeling the actual problem was probably political. The name is also a bit... well. As many children will prefer to avoid the use of profanity while raising their parents, I wonder if I shouldn't start by forking it and calling it the Big Furry Scheduler or something...
>> 
>> Anyhow this sheds lots of light on things. Thank, Eliot!
>> 
>> 
>> On Thu, Apr 18, 2013 at 1:29 PM, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>>  
>> Hi Casey,
>> 
>> On Thu, Apr 18, 2013 at 5:37 AM, Casey Ransberger <casey.obrien.r at gmail.com> wrote:
>>  
>> Totally. I know it isn't going to be a small thing. I'm curious if any of the BSD implementations solve the problem adequately for Cog; I might have something working to study, build tests around, etc. A control group.
>> 
>> The technical problem was solved for Linux in 2009 by Con Kolivas with his (excuse the language) http://en.wikipedia.org/wiki/Brain_Fuck_Scheduler.  The political problem of getting it adopted throughout the linux community so it can be relied upon is an entirely different thing.
>> 
>> Note that once BFS is more widely available I could write a VM that will test thread priorities on startup and use threads if multiple priorities are supported, falling back on the ITIMER if not.
>>  
>> 
>> Either way though, it would be a largish win for the community, given the widespread popularity of Linux. I might be able to find some friends who might like to attack it with me. Etcetera.
>> 
>> I wonder about why the Linux folks haven't dealt with it already. Maybe it hasn't come up. Hopefully it isn't a security thing, that'd be hard to make a case about.
>> 
>> Either way, I haven't figured out where to start looking yet.
>> 
>> 
>> On Thu, Apr 18, 2013 at 5:23 AM, David T. Lewis <lewis at mail.msen.com> wrote:
>> 
>> I think that Eliot has described the issue in some detail either on
>> this list, or on his blog http://www.mirandabanda.org/cogblog/. Sorry
>> I don't have any links handy, but reading through the blog is time
>> well spent in any case :)
>> 
>> I think you are dealing with a fundamental issue in the pthreads
>> implementation(s) on Linux, so don't be surprised if it's not just
>> a simple matter of fixing a bug. The pthreads implementation is more
>> or less grafted onto the original Unix process model, and operating
>> systems tend to vary as to whether they support pthreads fully, or
>> for that matter whether they support a thread model at all.
>> 
>> Dave
>> 
>> On Thu, Apr 18, 2013 at 05:07:42AM -0700, Casey Ransberger wrote:
>> >
>> > Well I guess maybe I left a part of the message out. Oops. I'm talking
>> > about Cog's heart. It needs user-level thread prioritization and apparently
>> > (GNU/?)Linux lacks this.
>> >
>> > My guess is it's a kernel issue. But that's an uneducated guess.
>> >
>> > It became interesting to me because I'm not super happy with the UI
>> > responsiveness of Squeak trunk under the interpreter and Raspbian on a
>> > 700MHz Pi (out of box experience isn't overclocked, so I'm targeting that.)
>> > My thought was to get the stack VM going, but we still have this issue with
>> > the heartbeat for the stack VM to be able to perform optimally. If I can
>> > fix the heartbeat (read: pthreads) issue, I can benefit GNU/Linux users of
>> > the system across the board, both in terms of the (Intel) JIT, and in terms
>> > of the stack oriented virtual machine which has the awesome Ungar-style
>> > garbage collection, right? I want the efficient GC eventually anyway. The
>> > advantages of stack orientation are somewhat beyond my current
>> > understanding of virtual machines, but I gather that's desirable as well?
>> > </noob>
>> >
>> > I need to do some tests with Cuis, Spoon, Pharo, and Etoys before I'm going
>> > to blame any part of the VM about the UI perf I'm seeing, but a faster VM
>> > is a faster VM anyway. I'd like to make all of the images faster on this
>> > little gadget, because it's cool, it's popular, and it gives us an approach
>> > on more than just the third world (not that the third world isn't
>> > incredibly important, just that if we don't start making better adults
>> > where people with first world problems are too, I'll end up feeling like
>> > Rick Moranis in Spaceballs or I'm going to have to relocate to someplace
>> > where we previously made better adults.)
>> >
>> > http://www.youtube.com/watch?v=sen8Tn8CBA4
>> >
>> > I know this isn't really the place to ask, but I thought maybe someone
>> > might be able to point me at what I'd need to dig into to understand the
>> > problem we have with the popular Linux implementation of pthreads, because
>> > when I GOOG that, I get #1 a tutorial on using pthreads, #2 a Wikipedia
>> > article which speaks abstractly about pthreads, and #3 another tutorial on
>> > using pthreads. I think I'm trying to figure out what to google for so that
>> > I can figure out where the problem lives and then look at it to see whether
>> > or not I can steal its lunch money.
>> >
>> > Even if I google "linux pthreads" I still get a tutorial on using them as
>> > the top hit.
>> >
>> > This is the most directly informative thing I can find:
>> >
>> > http://man7.org/linux/man-pages/man7/pthreads.7.html
>> >
>> > Hopefully this explains anything I might have left out of my first message
>> > on the subject!
>> >
>> > Casey
>> >
>> >
>> > On Wed, Apr 17, 2013 at 5:33 AM, David T. Lewis <lewis at mail.msen.com> wrote:
>> >
>> > >
>> > > On Wed, Apr 17, 2013 at 01:15:45AM -0700, Casey Ransberger wrote:
>> > > >
>> > > > I'm assuming the problem is in the kernel, but making assumptions is
>> > > usually a bad plan, so I'm asking.
>> > > >
>> > > > When I look, I find a rather confusing jumble: pthreads exists in
>> > > different implementations under different operating systems.
>> > > >
>> > > > I'd kind of like the heartbeat to work right under Raspbian, because
>> > > kids are going to use it, and the goal of producing better adults is pretty
>> > > close to my heart. See also making Squeak faster. (Stack VM.)
>> > > >
>> > > > I want to arm myself with as much knowledge about this as possible,
>> > > because I'm considering just bloody fixing it. If the (GNU/Linux) community
>> > > has objections, and I'm able to pull off the fix, I can make a patch
>> > > available to people who want it.
>> > > >
>> > > > I'm not confident that I can fix the bug with the knowledge I have now,
>> > > but I'm confident that I can fix it eventually, if someone else doesn't
>> > > beat me to the punch.
>> > > >
>> > > > Outside of the wiki page, are there any documents/people/mailing lists I
>> > > should look at to be able to get a good handle on where in the kernel (or
>> > > elsewhere) I should be looking for the code which isn't meeting our
>> > > Cog-nitive requirements?
>> > > >
>> > >
>> > > I do not understand what problem or bug you are asking about. Is there
>> > > some issue with Raspbian Linux that is causing a problem?
>> > >
>> > > Dave
>> > >
>> 
>> 
>> 
>> 
>> -- 
>> Casey Ransberger
>> 
>> 
>> 
>> 
>> -- 
>> best,
>> Eliot
>> 
>> 
>> 
>> 
>> -- 
>> Casey Ransberger
> 
> 
> 
> 
> 
> -- 
> best,
> Eliot

- Bert -

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