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Re: [Xen-devel] CONFIG_SMP required for save/restore and migration: bug?

Ian, Konrad, thanks for your replies. Here are some more details.

Il giorno 27/ago/2013, alle ore 15:33, Konrad Rzeszutek Wilk 
<konrad.wilk@xxxxxxxxxx> ha scritto:
> Are these PVHVM or PV domUs?
These are vanilla and recent linux kernels, directly loaded by Xen (no hvm 
loader): should be plain PV domUs.

Il giorno 27/ago/2013, alle ore 10:54, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
ha scritto:
> Can you diff the working and non-working configs to see if anything has 
> become implicitly (de)activated by changing the CONFIG_SMP setting?
Enabling SMP will generate some diff lines, mainly because on UP you're forced 
to use the TINY rcu and on SMP you're forced to use something else (TREE being 
the only remaining choice nowadays).

This is my good old trusty (and rusty) non-SMP config, from a vanilla 
kernel.org 3.10.9 source: http://pastebin.com/B7pC3gaC
It will hang like I described if you do xm save / xm restore on a node or try 
to migrate between nodes.

If you go in make menuconfig, turn on SMP support, change localversion, and do 
nothing else, you end up with this diff: http://pastebin.com/g0syXCVe
And the resulting SMP kernel will save/restore and migrate just fine.

These kernels do not use nor support loadable modules, and you will need an 
Intel CPU of the "Core" series or newer to run them - no Intel <= Pentium4 nor 
AMD processors.

I compile them with gcc (Gentoo Hardened 4.6.3 p1.13, pie-0.5.2) 4.6.3 
installed from Gentoo portage.
My Xen hosts are 64bit Xen 4.3.0 installed from Gentoo portage with the same 
gcc as the kernels.
Hypervisor command line is "watchdog nmi=dom0 com2=57600,8n1 vga=gfx-640x480x32 
console=com2,vga dom0_max_vcpus=1 dom0_vcpus_pin dom0_mem=2048M tmem tmem_dedup 

I tested them with a config like this:
# --------
name   = "foo"
kernel = "/srv/xen/images/bzImage-3.10.9-domU-UP"
memory = 1280
vcpus  = 1
vif    = [ 'bridge=bridge0', 'bridge=bridge1' ]
disk   = [ 'phy:/dev/mapper/foo,xvda,w' ]
root   = "/dev/xvda1 ro"
# --------

Note #1: yes I tested with vcpus=1 even with the SMP kernel
Note #2: I usually run them with extra="tmem" and while I can see it actually 
using tmem, it does not change the ability (or lack thereof) to restore/migrate.

I can provide the resulting binaries if anyone wants them, but I 
suspect/guess/hope it will be easily reproducible by others compiling their own 
I should be able to test the same kernels on an Ubuntu-shipped Xen sometime in 
the future, but not in the next days.

Luca Lesinigo

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