"High" cpu usage when using ZFS cache device

Artem Belevich art at freebsd.org
Tue Oct 11 21:14:09 UTC 2011

On Tue, Oct 11, 2011 at 1:17 PM, Steven Hartland
<killing at multiplay.co.uk> wrote:
>> It's a bummer. If you can build your own kernel cherry-picking
>> following revisions may help with long-term stability:
>> r218429 - fixes original overflow causing CPU hogging by l2arc feeding
>> thread. It will keep you up and running for longer until you hit
>> another overflow. If I remember correctly, it will hit you around
>> 100-days of uptime.
> This is the main issue we have been keeping an eye out for as we've
> seen it several times, we don't have too many machines with L2ARC so
> was surprised to see this with just 26 days up time in this case.
>> Following changes were done after ZFSv28 import, so they will not
>> apply directly to 8-RELEASE, but the idea applies to ZFSv15 as well.
>> The changes should be easy to backport.
>> r223412 - avoids more early overflows in time routines.
>> r224647 - avoids time overflow in TXG processing.
> We already maintain a custom set of patches for our 8.2 installs so
> shouldn't be an issue to add these so thanks for the info :)
> With all three should we expect no uptime overflow issues or still are
> we still going to look at ~100 day reboots required?

Those should get you through the known (to me) sources of LBOLT and
clock_t related overflows.
Can't say whether you'll run into some other problems.


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