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SubjectRe: [PATCH] O13int for interactivity


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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