Re: responsiveness during IO tasks

Doug Barton wrote:
> On 04/26/2011 03:37, Alexander Best wrote:
>> On Mon Apr 25 11, Steve Wills wrote:
>> I've noticed lately that when doing heavy IO, my 9-CURRENT system (Fri
>> Apr 15 23:33:46 EDT 2011) is quite unresponsive. I have two ZFS mirrors
>> setup and run KDE4. The system has 12GB of RAM.
>>
>> When I, for example, copy an ISO image from one mirror to the other, the
>> whole desktop becomes really slow during the copy. It takes a good 15
>> seconds to open a new tab in Konsole, switching windows takes a while,
>> etc. Once the copy is finished, things are fine. It wasn't like this
>> back before I upgraded from 8.2-RC1 to 9-CURRENT. Has anyone else
>> noticed something similar, or is it just me? Is there any other info I
>> can provide or something I should look for?
>>
>>> i've noticed this too. for me the situation is sometimes even worse.
>>> during
>>> heavy i/o the mouse cursor won't even respond.
>>
>>> i think this is a scheduler isse. maybe running a non-preemptive
>>> kernel or
>>> switching to the old 4bsd scheduler fixes it?
> 
> Try backing up your src tree to r212540, clean /usr/obj,
> buildworld/kernel and see if that helps. I just tracked down a big part
> of my current problem (pun intended) to r212541, the one-shot timer
> commit. I'm working on a larger post to describe my problems, but short
> version is, up through r212540 I can load the system down as heavily as
> I want, and while there may be some unresponsiveness it's at least
> stable. If I update to one-shot timers the system wedges as soon as I
> put load on it. No panic, not even a reboot, it just wedges solid
> requiring it to be powered off.
> 
> You should also test SCHED_4BSD to see if that improves your situation.
> There have been a lot of reports about problems with SCHED_ULE with
> heavy disk i/o. Moving to 4bsd helps me in terms of interactivity, but I
> needed to find the crashing problem first.
> 
> Doug (sorry mav)

No problem, just let's hunt things down. I'll wait for that larger post.
In meantime, if it is related to eventtimers, it would be good to
collect more detailed information. You could try to make timer run
during idle (kern.eventtimer.idletick). You could try to switch timer
from one-shot to periodic mode (kern.eventtimer.periodic). You could
also try to switch to another timer (kern.eventtimer.timer).

-- 
Alexander Motin