On Mon, 7 Aug 2017, Paolo Bonzini wrote:

On 01/08/2017 23:38, Dominik 'Rathann' Mierzejewski wrote:
On Tuesday, 01 August 2017 at 14:19, Florian Weimer wrote:
We still build a special glibc variant for Xen which avoids certain
segment-relative accesses which are difficult to emulate with
paravirtualization..

Is this still needed?  Can we drop it?
What is the performance difference between running a regular glibc under
Xen vs. this special one? I believe there may still be some value in
running Fedora in a Xen i686 guest VM.

The performance difference was very significant, though like others I
cannot really give a figure.

However, it only applied if you were running in a 32-bit hypervisor.  I
think this set up is pretty much dead.  Even though Amazon and others
are using Xen and are still running paravirtualized guests, they're
using 64-bit hypervisors.  CCing Vitaly for confirmation.

The 32-bit (x86) hypervisor was dropped in xen-4.3.0 and as xen-4.4.x and earlier are end-of-life, the workaround presumably isn't needed now if it was just with the 32-bit hypervisor.

        Michael Young
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