Re: [PATCH] O13int for interactivity

[Nick Piggin]

Nick Piggin wrote:

> Mike Galbraith wrote:
>
> > At 12:51 PM 8/12/2003 +1000, Nick Piggin wrote:
> >
> >
> > > Rob Landley wrote:
> > >
> > > > On Tuesday 05 August 2003 06:32, Nick Piggin wrote:
> > > >
> > > >
> > > > > But by employing the kernel's services in the shape of a blocking
> > > > > syscall, all sleeps are intentional.
> > > >
> > > >
> > > >
> > > > Wrong.  Some sleeps indicate "I have run out of stuff to do right 
> > > > now, I'm going to wait for a timer or another process or something 
> > > > to wake me up with new work".
> > > >
> > > >
> > > >
> > > > Some sleeps indicate "ideally this would run on an enormous ramdisk 
> > > > attached to gigabit ethernet, but hard drives and internet 
> > > > connections are just too slow so my true CPU-hogness is hidden by 
> > > > the fact I'm running on a PC instead of a mainframe."
> > >
> > >
> > >
> > > I don't quite understand what you are getting at, but if you don't 
> > > want to
> > > sleep you should be able to use a non blocking syscall. But in some 
> > > cases
> > > I think there are times when you may not be able to use a non 
> > > blocking call.
> > > And if a process is a CPU hog, its a CPU hog. If its not its not. 
> > > Doesn't
> > > matter how it would behave on another system.
> >
> >
> >
> > Ah, but there is something there.  Take the X and xmms's gl thread 
> > thingy I posted a while back.  (X runs long enough to expire in the 
> > presence of a couple of low priority cpu hogs.  gl thread, which is a 
> > mondo cpu hog, and normally runs and runs and runs at cpu hog 
> > priority, suddenly acquires extreme interactive priority, and X, 
> > which is normally sleepy suddenly becomes permanently runnable at cpu 
> > hog priority)  The gl thread starts sleeping because X isn't getting 
> > enough cpu to be able to get it's work done and go to sleep.  The gl 
> > thread isn't voluntarily sleeping, and X isn't voluntarily running.  
> > The behavior change is forced upon both.
>
>
>
> It does... It is I tell ya!
>
> Look, the gl thread is probably _very_ explicitly asking to sleep. No I
> don't know how X works, but I have an idea that select is generally used
> as an event notification, right?
>
> Now the gl thread is essentially saying "wait until X finishes the work
> I've given it, or I get some other event": ie. "put me to sleep until
> this fd becomes readable".
>
> OK maybe your scenario is a big problem. Its not due to any imagined
> semantics in the way things are sleeping. Its due to the scheduler.


And no, X isn't intentionally sleeping. Its being preempted which is
obviously not intentional.

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