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

[Jeff Garzik <jgarzik@pobox.com>]

Andrea Arcangeli wrote:
> On Tue, Oct 05, 2004 at 11:27:06PM -0400, Jeff Garzik wrote:
> 
>>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.
> 
> 
> well, you are assuming those latencies are visible with eyes. they might
> be in extreme cases, but normally they're not (what people notices
> normally are disk latencies, and few people uses an RT userspace
> anyways which means they cannot claim the problem to be a lack of
> cond_resched, but more likely they want shorter timeslices in the
> scheduler etc..). So my point is that you need a measurement tool anyways...


I do agree with that.

I don't think that implies preempt is useful for anything except hiding 
stuff that should be fixed anyway, though...

Preempt will always be something I ask people to turn off when reporting 
driver bugs; it just adds too much complicated mess for zero gain.

	Jeff