openstack team mailing list archive

[Armando Migliaccio <Armando.Migliaccio@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: Eric Windisch [mailto:eric@xxxxxxxxxxxxxxxx]
> Sent: 02 March 2012 19:04
> To: Joshua Harlow
> Cc: Armando Migliaccio; Jay Pipes; openstack
> Subject: Re: [Openstack] eventlet weirdness
> 
> The problem is that unless you sleep(0), eventlet only switches context when
> you hit a file descriptor.
> 
> As long as python coroutines are used, we should put sleep(0) where-ever it is
> expected that there will be a long-running loop where file descriptors are not
> touched. As noted elsewhere in this thread, MySQL file descriptors don't
> count, they're not coroutine friendly.
> 
> The premise is that cpus are pretty fast and get quickly from one call of a
> file descriptor to another, that the blocking of these descriptors is what a
> CPU most waits on, and this is an easy and obvious place to switch coroutines
> via monkey-patching.
> 
> That said, it shouldn't be necessary to "sprinkle" sleep(0) calls. They should
> be strategically placed, as necessary.

I agree, but then the whole assumption of adopting eventlet to simplify the programming model is hindered by the fact that one has to think harder to what is doing...Nova could've kept Twisted for that matter. The programming model would have been harder, but at least it would have been cleaner and free from icky patching (that's my own opinion anyway).

> 
> "race-conditions" around coroutine switching sounds more like thread-safety
> issues...
> 

Yes. There is a fine balance to be struck here: do you let potential races appear in your system and deal with them on a case-by-case base, or do you introduce mutexes and deal with potential inefficiency and/or deadlocks? I'd rather go with the former here.

> --
> Eric Windisch
> 
> 
> On Friday, March 2, 2012 at 1:35 PM, Joshua Harlow wrote:
> 
> > Re: [Openstack] eventlet weirdness Does anyone else feel that the following
> seems really “dirty”, or is it just me.
> >
> > “adding a few sleep(0) calls in various places in the Nova codebase
> > (as was recently added in the _sync_power_states() periodic task) is
> > an easy and simple win with pretty much no ill side-effects. :)”
> >
> > Dirty in that it feels like there is something wrong from a design point of
> view.
> > Sprinkling “sleep(0)” seems like its a band-aid on a larger problem imho.
> > But that’s just my gut feeling.
> >
> > :-(
> >
> > On 3/2/12 8:26 AM, "Armando Migliaccio" <Armando.Migliaccio@xxxxxxxxxxxxx>
> wrote:
> >
> > > I knew you'd say that :P
> > >
> > > There you go: https://bugs.launchpad.net/nova/+bug/944145
> > >
> > > Cheers,
> > > Armando
> > >
> > > > -----Original Message-----
> > > > From: Jay Pipes [mailto:jaypipes@xxxxxxxxx]
> > > > Sent: 02 March 2012 16:22
> > > > To: Armando Migliaccio
> > > > Cc: openstack@xxxxxxxxxxxxxxxxxxx
> > > > Subject: Re: [Openstack] eventlet weirdness
> > > >
> > > > On 03/02/2012 10:52 AM, Armando Migliaccio wrote:
> > > > > I'd be cautious to say that no ill side-effects were introduced.
> > > > > I found a
> > > >
> > > > race condition right in the middle of sync_power_states, which I
> > > > assume was exposed by "breaking" the task deliberately.
> > > >
> > > > Such a party-pooper! ;)
> > > >
> > > > Got a link to the bug report for me?
> > > >
> > > > Thanks!
> > > > -jay
> > >
> > >
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