Thanks Jimmy for your help,
It appears that apt-mark hold and aptitude hold have same effects, you could obtain the same with some tricks with dpkg.I would use 'apt-mark'. # apt-mark hold 'package-name' and # apt-mark unhold 'package-name'
If I used apt-get, it should be wise to use apt-mark. When using only aptitude (my choice), it seems I must use aptitude hold to remain consistent (using apt-get or aptitude is an old, and perhaps unclear, war ;)))
By the way I've found what is the kaiser patch (inducing performance loss between 5% -mean use- and 30% -a heavy network load-) and why (in my context only, see previous message) I should use nokaiser option (https://lwn.net/Articles/737940) and, thanks to fine people here, the nopti option.network link
On an almost idle workstation the effects of using theses options are not really visible (tested). But on a huge Xeon 64Go ram 2x2To raid1/lvm/debian 8/Xen 4 with 1 Gbps network and more than twenty VM, definitly not the same story (some friends has done some tests on their less loaded than mine dedicated servers and the performance loss is really huge). I have some low cost spare dedicated servers and will proceed to some tests too.
Stef All the best from Oleron island,