[dm-crypt] dm-crypt kills NFS performance?

Arno Wagner arno at wagner.name
Thu Apr 21 22:26:47 CEST 2011

On Thu, Apr 21, 2011 at 08:06:25PM +0200, Milan Broz wrote:
> On 04/21/2011 07:52 PM, Arno Wagner wrote:
> > 
> > This sounds like one more problems with the Big Kernel Lock.
> > The basic problem (simplified) is that some operations
> > block everything while running. dm-crypt and RAID makes 
> > them take longer, but the problem is the blocking. 
> It can be many problems, from network card driver to
> nfs handling or io scheduler setting.
> For dm-crypt (kcryptd) - it doesn't not use BKL at all
> and after every sector encryption it calls cond_resched()
> (hinting scheduler to switch process if there is other work
> even if kernel is compiled with voluntary preemption).
> So it should behave correctly under load.

Ah. Good to know. 

Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name 
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