On Tue, Aug 01, 2017 at 11:38:45PM +0200, 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?
This is a sort of historical feature. I had only a vague memory of this from when I last used Xen PV & 32 bit guests (which must have been around 2005?), but the precise problem and solution is explained in these pages on the old XenSource wiki: https://web.archive.org/web/20080421123834/http://wiki.xensource.com:80/xenwiki/XenSegments https://web.archive.org/web/20080218095938/wiki.xensource.com/xenwiki/XenSpecificGlibc Note the binaries for Fedora Core 3 :-) > 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. I seem to recall that the performance penalty was very significant. However, note that this is only for using Xen paravirtualization. In no way would dropping this prevent you from using Xen or 32 bit i686 guests, but you would have to use full virtualization. That requires hardware virt, but (almost literally) every Intel and AMD processor since 2006 has shipped with hardware virt. Also this doesn't apply to 64 bit guests at all (even PV) since they didn't have to do fun things with segment registers to protect the hypervisor from the guest. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org
