[PTLsim-devel] better guest SMP support?

Thu Oct 18 12:51:23 EDT 2007

Hi all,

I've recently been looking at Xen web page, KVM, etc...
Seems that they all have problems with guest SMPs:

For example:

----- (copy&paste)
SMP Guests
The current HVM code only stably supports uniprocessor guests, though 
work is underway to robustify SMP guest support. Xen already contains 
APIC and IOAPIC emulation modules, but this code along with the existing 
shadow pagetable code lacks synchronization in certain places. The new 
shadow mode code should go a long way to solving this. Work is also 
ongoing to add ACPI BIOS support, hence allowing the emulated platform 
to look like a modern PC. The first aim for supporting SMP guests is 
correctness, and once we have that focus on performance and scalability. 
Getting fair performance for two and four way guests should be 
achievable for many workloads, but this is an area where 
paravirtualization really helps. Eventually, it would be good to support 
CPU hotplug emulation in Xen.
-----
I don't know how stable is SVM part of the Xen. I've seen on mailing 
lists that is sometimes blocks without reason (probably due to some 
deadlock or something similar).

KVM: the support for guest SMPs was added just recently, with the new 
2.6.23 kernel, so it also _has_ to be unstable for some time.

On the other hand, both Xen and KVM are based on the QEMU, which has a 
kqemu - kernel module for the acceleration, and very good guest SMP 
support. I ran 128 guest cpus on my T60 dual core laptop, without any 
problems, and with very very good performance.
The biggest problem was the Linux kernel which had trouble running on 
this many cores. After using the latest available kernel version, the 
booting was successful, with all 128 cores :)

The question is: are there any attempts to run kqemu + QEMU + PTLsim, 
i.e. to port the PTLsim to QEMU?
The installation of kqemu + QEMU is very straightforward, easy and fast.
kqemu installs without even rebooting the machine (requires root account 
for the installation), and doesn't require root access to run, after the 
installation is successful.
QEMU itself doesn't require root account, for compiling, installing or 
running, but it has very bad performance if it is used without kqemu.

-- 
Saša Tomić
BSC - Barcelona Supercomputing Center
c\ Jordi Girona 29, Nexus I, 08034 Barcelona, España
Tel.: ,  
http://www.bsc.es

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 3237 bytes
Desc: S/MIME Cryptographic Signature
Url : https://ptlsim.org/pipermail/ptlsim-devel/attachments/20071018/dbbfe195/attachment.bin 