Re: repeatable hang with loop mount and heavy IO in guest

[RW <kvm@tauceti.net>]

No sorry, I haven't any performance data with noop. I even don't
have had a crash. BUT I've experienced serve I/O degradation
with noop. Once I've written a big chunk of data (e.g. a simple
rsync -av /usr /opt) with noop it works for a while and
after a few seconds I saw heavy writes which made the
VM virtually unusable. As far as I remember it was kjournald
which cases the writes.

I've written a mail to the list some months ago with some benchmarks:
http://article.gmane.org/gmane.comp.emulators.kvm.devel/41112/match=benchmark
There're some I/O benchmarks in there. You can't get the graphs
currently since tauceti.net is offline until monday. I haven't
tested noop in these benchmarks because of the problems
mentioned above. But it compares deadline and cfq a little bit
on a HP DL 380 G6 server.

Robert

On 01/21/10 22:08, Thomas Beinicke wrote:
> On Thursday 21 January 2010 21:08:38 RW wrote:
>> Some months ago I also thought elevator=noop should be a good idea.
>> But it isn't. It works good as long as you only do short IO requests.
>> Try using deadline in host and guest.
>>
>> Robert
> 
> @Robert: I've been using noop on all of my KVMs and didn't have any problems 
> so far, never had any crash too.
> Do you have any performance data or comparisons between noop and deadline io 
> schedulers?
> 
> Cheers,
> 
> Thomas
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