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SubjectRe: [PATCH] O13int for interactivity


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.


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