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Re: NSRunLoop Tidying


From: Dr. H. Nikolaus Schaller
Subject: Re: NSRunLoop Tidying
Date: Sat, 9 Oct 2010 13:49:46 +0200

Am 09.10.2010 um 13:19 schrieb David Chisnall:

>  meaning that we spend a lot more time sleeping in userspace waiting for the 
> kernel to wake us up

Let me ask a fundamental question: do we really have a performance problem to 
solve here?
Are any measurements available that a typical application spends more than some 
% in this code?

In my understanding, the timers and the untilDate: are handled only once per 
loop and then the kernel sleeps. Sometimes for minutes until the user moves the 
mouse or clicks a key. The same will happen with any alternative mechanism. I 
think your proposal will only simplify calculation how long to sleep and 
setting up the kernel to do so. But not improve the sleep time.

The only situation where I can see that setting up the triggers as fast as 
possible is if you have timers that expire in fractions of milliseconds. But do 
we have a single example where this is required? Another area could be file 
handles for network stacks. Do we have a performance bottleneck there?

I have a little the impression that the proposal is just for clearness of the 
code or "innovation" for innovation's sake?
I fear a little by leaving POSIX we deviate from the least common denominator 
of all UNIX systems and introduce more dependencies.

I don't want to argue against innovation, but it must really improve something.

So I would propose that you work on a code branch that demonstrates that it 
works (better).

Best regards,
Nikolaus


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