Wind River Support Network


LIN8-4629 : Request to build lvm2 without "--disable-o_direct"

Created: Sep 6, 2016    Updated: Dec 3, 2018
Resolved Date: Oct 10, 2016
Found In Version:
Fix Version:
Severity: Standard
Applicable for: Wind River Linux 8
Component/s: Kernel



In WRL8 (and also earlier WRL releases) lvm2 is built with the --disable-o_direct flag. 
We notice quite some degradation in performance with o_direct disabled. 
If enabled we get much better performance. 

Why is it disabled? 
Is there any risk with enabling it? 
Can you enable it as default? 

In WRL6 it was also disabled, but the code in lvm2 was changed in WRL8 to be a lot more aggressive with its sync operations. 
Now it seems to call sync operations on block device level, that takes time. 

Looking at git history in yocto it seems that is comes from long back in time, so maybe this is some flag that was needed back then but is obsolete and not needed any more. 

We have not done very much testing yet, but so far we have not noticed any regression with enabling it. 

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