On 12/13/21 16:21, Heiko Carstens wrote:
On Mon, Dec 13, 2021 at 03:26:58PM +0100, Pierre Morel wrote:
Why is this assumption necessary? The statement that Linux runs only
with horizontal polarization is not true.
Right, I will rephrase this as:
"Polarization change is not taken into account, QEMU intercepts queries for
polarization change (PTF) and only provides horizontal polarization
indication to Guest's Linux."
@Heiko, I did not find any usage of the polarization in the kernel other
than an indication in the sysfs. Is there currently other use of the
polarization that I did not see?
You can change polarization by writing to /sys/devices/system/cpu/dispatching.
Or alternativel use the chcpu tool to change polarization. There is
however no real support for vertical polarization implemented in the
kernel. Therefore changing to vertical polarization is _not_
recommended, since it will most likely have negative performance
impacts on your Linux system.
However the interface is still there for experimental purposes.
Thanks, so I guess that not reflecting polarization changes to the guest
topology will be OK for the moment.
Of course, I will change the wrong comment.
--
Pierre Morel
IBM Lab Boeblingen
