Re: 2.6.36 io bring the system to its knees

[Corrado Zoccolo <czoccolo@gmail.com>]

On Sun, Oct 31, 2010 at 3:31 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Sat, Oct 30, 2010 at 07:02:35PM +0600, Aidar Kultayev wrote:
>> the system is/was doing :
>> .dd if=/dev/zero of=test.10g bs=1M count=10000;rm test.10g
>> .netbeans
>> .compiling gcc-4.5.1
>> .running VBox, which wasn't doing any IO. The guest os was idle in other words
>> .vlc
>> .chromium
>> .firefox
>> and bunch of other small stuff.
>>
>> Even without having running DD, the mouse cursor would occasionally
>> lag. The alt+tab effect in KWin would take 5+seconds to workout.
>> When I run DD on top of the workload it consistently made system much
>> more laggy. The cursor would freeze much more frequent. It is like if
>> you drag your mouse physically, but the cursor on the screen would
>> jump discretely, in other words there is no continuity.
>> Music would stop.
>
> If you start shutting down tasks, Vbox, netbeans, chromium, etc., at
> what point does the cursor start tracking the system easily?  Is the
> system swapping?  Do you know how to use tools like dstat or iostat to
> see if the system is actively writing to the swap partition?  (And are
> you using a swap partition or a swap file?)
>
> The fact that cursor isn't tracking well even when the dd is running,
> and presumably the only source of I/O is the gcc and vlc, makes me
> suspect that you may be swapping pretty heavily.  Have you tried
> investigating that possibility, and made sure it has been ruled out?

Something to try is also to raise X cpu scheduling priority, since I
would be really surprised if we evict from memory the routine that
draws the cursor.
BTW, I've seen the cursor jumping problem even when not swapping, and
with minimal *real* disk activity (but with heavy usage of a fuse
filesystem providing remote resources), and high cpu activity.
Raising X priority solved the problem with the mouse pointer, but the
gui programs still didn't respond quickly...

Thanks
Corrado

>
>                                                - Ted
>
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