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

[Nick Piggin]

Robert Love wrote:
> On Tue, 2004-10-05 at 21:55 -0400, Jeff Garzik wrote:
>
>
> > As opposed to fixing drivers???  Please fix the drivers and code first.
>
>
> No, definitely not, dude.  Fixes for anything--drivers include--is never
> superseded by anything else, even the eternal quest for "low latency." 
>
>
> > > sprinkling cond_resched() hacks all over the kernel.
> >
> > cond_resched() is not the only solution.
>
>
> Indeed.  Most other solutions (fixing algorithms, lowering lock hold
> time) have "automatic" benefits with kernel preemption, though, and that
> has been what I have always advocated.

Well, but then without preempt, you *still* need to put cond_rescheds
in non-critical-section code. So cond_resched really does seem to be
the only solution (other than preempt).

I think this is why Ingo found he needed a check in might_sleep to get
really good latency (again, I could be wrong here as I haven't been
really following the progress of that work). But imagine when you
unwind *that* hack into the callers. Yuck.
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