Re: [patch] zfs livelock and thread priorities

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
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