Sawtooth in disk I/O performance graph after Xenserver 7 upgrade

After upgrading to Xenserver 7.0, we realized disk performance graph has a constant sawtooth pattern of up to 1GB/s.
This happen in all our environments and with VMs in both Windows ( 2008R2, 2012, 2012R2 ) and Linux (Ubuntu 14.04 HVM or Ubuntu 14.04 PV) as soon as we turn on VM on disk where operating system is installed.
Same VMs with Xenserver 6.5 didn't experienced this issue.

Only one VM does not show this behaviour:

• Xenserver DDK VM imported from ISO.

However, there is no I/O at dom0 level (network level, since VDIs are remotely stored via NFS).

Could this be related with new tapdisk polling?