"High" cpu usage when using ZFS cache device

Steven Hartland killing at multiplay.co.uk
Tue Oct 11 20:17:51 UTC 2011

----- Original Message ----- 
From: "Artem Belevich" <art at freebsd.org>

> On Tue, Oct 11, 2011 at 10:21 AM, Steven Hartland
> <killing at multiplay.co.uk> wrote:
>> Thanks for the confirmation there Artem, we currently can't use 8-STABLE
>> due to the serious routing issue, seem like every packet generates a
>> RTM_MISS routing packet to be sent, which causes high cpu load.
>> Thread: "Re: serious packet routing issue causing ntpd high load?"
> 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?


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