Messages in this thread | | | Date | Tue, 12 Aug 2003 11:22:25 +0200 | From | Mike Galbraith <> | Subject | Re: [PATCH] O13int for interactivity |
| |
At 05:07 PM 8/12/2003 +1000, 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?
Oh, sure, it blocks because it asks for it... but not because it _wants_ to :) It wants to create work for X fast enough to make a nice stutter free bit of eye-candy.
>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".
Yes. Voluntary or involuntary is just a matter of point of view.
>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.
It's due to the scheduler to a point... only in that it doesn't recognize the problem and correct it (that might be pretty hard to do). If my hardware were fast enough that X could get the work done in the allotted time, the problem wouldn't arise in the first place. I bet it's fairly hard to reproduce on a really fast box. It happens easily on my box because the combination of X and the gl thread need most of what my hardware has to offer.
-Mike
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |