On Wednesday, 02 August 2017 at 14:42, Richard W.M. Jones wrote: > 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. Thanks for the web archive links. Unfortunately, they don't quantify the penalty, either. I'd feel more confident if I knew what it was (e.g. 10x slower or 1.1x slower?) > 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. Right, so the use-case seems to be pretty limited. I'd say announce the intention to drop, publicize it widely and see what the feedback is. If almost nobody complains, then I'd say get rid of it if it makes life simpler. Regards, Dominik -- Fedora https://getfedora.org | RPMFusion http://rpmfusion.org There should be a science of discontent. People need hard times and oppression to develop psychic muscles. -- from "Collected Sayings of Muad'Dib" by the Princess Irulan _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx
