Re: responsiveness during IO tasks

On 04/26/2011 03:37, Alexander Best wrote:
> On Mon Apr 25 11, Steve Wills wrote:
> Hi,
>
> 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.


hth,

Doug (sorry mav)

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