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

Milan Broz mbroz at redhat.com
Thu Apr 21 20:06:25 CEST 2011


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.

Milan


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