[patch] zfs livelock and thread priorities

[Pegasus Mc Cleaft]

On Friday 17 April 2009 01:30:21 Ben Kelly wrote:
> On Apr 15, 2009, at 12:35 AM, Artem Belevich wrote:
> > I'll give it a try in a few days. I'll let you know how it went.
>
> Just FYI, I was able to reproduce some of the failures with the
> original patch using an SMP vmware image.  The new patch seems to fix
> these problems and I was able to successfully mount a zfs pool.
>
> > BTW, now that you're tinkering with ZFS threads and priorities, whould
> > you by any chance have any idea why zfs scrub is so painfully slow on
> > -current?
> > When I start scrub on my -stable box, it pretty much runs full speed
> > -- I can see disks under load all the time.
> > However on -current scrub seems to run in small bursts. Disks get busy
> > for a second or so and then things get quiet for about five seconds or
> > so and this pattern repeats over and over.
>
> I don't know.  I haven't had to scrub my devices very often.  I ran a
> couple here locally and did not see the behavior you describe.  There
> is a significant delay between typing zpool scrub and when it actually
> begins disk I/O, but after that it completes without pause.  If I get
> a chance I'll try to look at what the scrub code is doing.

Hi Ben, 

	I saw the same pausing of of a scrub on my machine as Artem is. It may be 
coincidence, but I had disabled the zil and prefetch. After I re-enabled the 
zil and prefetch, the pausing stopped and the scrub would complete without any 
stalling.  I never disabled the zil and prefetch to see if this was the true 
cause or not.. 

Peg