Hi, What is the difference between a kernel with Xen but not used (Dom0 node) and a kernel without Xen code at all? For distrib, it could be very important that we have a standard kernel *with* Xen even if 95% of users don''t use it (if the perf impact is null or low) so the 5% of the user that need/want Xen can use it out of the box without recompiling. So, is there a perf penalty if Xen is in the kernel? Thanks -jec _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Jean-Eric Cuendet wrote:> What is the difference between a kernel with Xen but not used (Dom0 > node) and a kernel without Xen code at all? > For distrib, it could be very important that we have a standard kernel > *with* Xen even if 95% of users don''t use it (if the perf impact is null > or low) so the 5% of the user that need/want Xen can use it out of the > box without recompiling.I don''t believe that would make sense. None of the distributions that I use (SuSE, Fedora, Ubuntu currently) come with only one kernel. All kernels are built for a specific architecture (i386, i586, i686, amd64, ppc, etc.) though some happen to be backward compatible. Most of the distributions will detect Athlon vs. Xeon, SMP versus UP, large vs. small amount of memory, etc. a kernel that is tweaked for that configuration will be installed (usually without the user having to specify). A Xen kernel will not run on any hardware that does not include Xen, perhaps the Xen kernel code could be made to be backwards compatible (run-time detection of Xen vs. non-Xen) but it doesn''t sound worthwhile to me.> So, is there a perf penalty if Xen is in the kernel?To run a Xen kernel you must also run the Xen hypervisor. There is overhead but it is generally very low especially when running only a single domain as you are suggesting. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Jean-Eric Cuendet wrote:> What is the difference between a kernel with Xen but not used (Dom0 > node) and a kernel without Xen code at all? > For distrib, it could be very important that we have a standard kernel > *with* Xen even if 95% of users don''t use it (if the perf impact is null > or low) so the 5% of the user that need/want Xen can use it out of the > box without recompiling.I don''t believe that would make sense. None of the distributions that I use (SuSE, Fedora, Ubuntu currently) come with only one kernel. All kernels are built for a specific architecture (i386, i586, i686, amd64, ppc, etc.) though some happen to be backward compatible. Most of the distributions will detect Athlon vs. Xeon, SMP versus UP, large vs. small amount of memory, etc. a kernel that is tweaked for that configuration will be installed (usually without the user having to specify). A Xen kernel will not run on any hardware that does not include Xen. Possibly the Xen kernel code could be made to be backwards compatible (run-time detection of Xen vs. non-Xen) but it doesn''t sound worthwhile to me.> So, is there a perf penalty if Xen is in the kernel?To run a Xen kernel you must also run the Xen hypervisor. There is overhead but it is generally very low especially when running only a single domain as you seem to be suggesting. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> Most of the distributions will detect Athlon vs. Xeon, SMP versus UP, > large vs. small amount of memory, etc. a kernel that is tweaked for that > configuration will be installed (usually without the user having to > specify).That''s the point of my question! Why would these distrib ship the *base* kernel *with* Xen directly, so no need for reboot if you want Xen: just start the hypervisor and go!> To run a Xen kernel you must also run the Xen hypervisor. There is > overhead but it is generally very low especially when running only a > single domain as you seem to be suggesting.So the question: what is the penalty if we run Xen *without* the hypervisor (so without virtual machines) -jec _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, Jan 09 ''06 at 12:24, Jean-Eric Cuendet wrote:> That''s the point of my question! Why would these distrib ship the *base* > kernel *with* Xen directly, so no need for reboot if you want Xen: just > start the hypervisor and go!The Hypervisor runes above (or below) the kernel (debending on how you view the layers in the whole sytem). But to work the Xen-Kernel NEEDS services the hypervisor provides. Without a hypervisor the xen-kernel will not boot.> So the question: what is the penalty if we run Xen *without* the > hypervisor (so without virtual machines)As it will not work at all, the palenty is infnit. -- Goetz Bock (c) 2006 as blacknet.de - Munich - Germany /"\ IT Consultant Creative Commons secure mobile Linux everNETting \ / X ASCII Ribbon Campaign against HTML email & microsoft attachments / \ _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users