[Linux-cluster] qdiskd eviction on missed writes

[Lon Hohberger]

On Thu, 2007-01-04 at 11:35 -0500, Lon Hohberger wrote:
> 
> Making the read/write separate probably will (probably) not change much
> - it's all direct I/O.  You basically said it yourself: on high end
> storage, this just shouldn't be a problem.  We're doing a maddening 8k
> of reads and 0.5k of writes during a normal cycle every (in your case) 1
> second.
> 
> So, I suspect it's a scheduling problem.  That is, it would probably be
> a whole lot more effective to just increase the priority of qdiskd so
> that it gets scheduled even during load spikes (E.g. use a realtime
> queue; SCHED_RR?).  I don't think the I/O path is the bottleneck.

I'll be working on a patch to allow you to turn on/off RT scheduling for
qdiskd from the configuration file (as well as other qdisk-related bits)
tomorrow and early next week -- would you like to test it when I get it
ready?

-- Lon
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