The snoop_filter was enabled by default by this change:
commit 080d4e08d6
Author: Andreas Hansson <andreas.hansson@arm.com>
Date: Fri Aug 12 14:11:45 2016 +0100
mem: Add snoop filter to SystemXBar by default
Change-Id: I850473c70437588b47812f1dc00d6ecdb66daa36
Reviewed-on: https://gem5-review.googlesource.com/2647
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>