Re: bonnie++ uninterruptible under heavy I/O load

[Fabio Coatti]

Alle 16:16, venerdì 11 marzo 2005, Jens Axboe ha scritto:
> On Fri, Mar 11 2005, Simone Piunno wrote:
> > Alle 14:29, venerdì 11 marzo 2005, Baruch Even ha scritto:
> > > echo t > /proc/sysrq-trigger
> >
> > Before killing bonnie:
>
> I'm guessing your problem is that bonnie dirtied tons of data before you
> killed it, so it has to flush it out. If you run out of request entries,
> you will get to sleep uninterruptibly on those while the data is
> flushing. I don't see anything unexpected here, it is normal behaviour.

The real issue here is that under heavy I/O activity (bonnie is a good way to 
emphasize the concept), even caused by only one task, the system becomes 
quite unresponsive and "sluggish". The same can be seen under a gentoo 
"emerge --metadata", and slocate has the same effect.
The problem is not only related to desktop, but i.e. on a dual opteron il 
takes several seconds to have an "ls" output (on a nearly empty dir) or 
simply to log in using ssh.
It seems to me that I/O scheduler gives high priority to the running process 
and any other request is delayed to the point that the responsiveness of a 
desktop becomes poor (say, to open a "K" menu takes several seconds on a pIV 
2.8G HT).
In every case, we seen that the I/O bound processes are stuck in "D" state, 
the same stands for pdflush and kswapd.


-- 
Fabio Coatti              Wireless Solutions SpA - DADA group   
Services Manager        Europe HQ, via Castiglione 25 Bologna 
http://www.wseurope.com     Tel: +390512966811 Fax: +390512966800
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