Re: Preempt? (was Re: Cannot enable DMA on SATA drive (SCSI-libsata,VIA SATA))

[Jeff Garzik]

Nick Piggin wrote:
> Jeff Garzik wrote:
>
> > Andrea Arcangeli wrote:
> >
> > > So I disagree with your claim that preempt risks to hide inefficient
> > > code, there are many other (probably easier) ways to detect inefficient
> > > code than to check the latencies.
> >
> >
> >
> >
> > You're ignoring the argument :)
> >
> > If users and developers are presented with the _impression_ that long 
> > latency code paths don't exist, then nobody is motivated to profile 
> > them (with any tool), much less fix them.
>
> But even without preempt you'd still have to profile the latency.

You're making my point for me.  If the bandaid (preempt) is not active, 
then the system can be accurated profiled.  If preempt is active, then 
it is potentially hiding trouble spots.

The moral of the story is not to use preempt, as it
* potentially hides long latency code paths
* potentially introduces bugs, as we've seen with net stack and many 
other pieces of code
* is simply not needed, if all code paths are fixed

	Jeff


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