What does Xen mean for you? Xen has less overhead compared to UML. Xen Linodes have 4 processors. They support kernel modules. They support 32 and 64 bit kernels. We’re running the latest Xen version (3.2.1) which means we can support paravirt_ops kernels (pv_ops), which means we can have kernels newer than 2.6.18 (which a lot of our competitors force you to use). In short, Linodes will be much, much faster under Xen.

From here on, all new host hardware will be deployed running Xen. New accounts should land on these machines, but there’s still a chance a new Linode will land on a UML host. If this happens, or you are already on a UML host and want to move over, just submit a ticket. However, it’s just a matter of time before all our machines are running on Xen — we’ll announce the upgrade schedule in the next few weeks.

=http://www.virtual-strategy.comVirtual Strategy Magazine[/url] speaks with Jeff Dike, author and maintainer of User-Mode Linux and Christopher Aker, president of Linode, a hosting company that offers virtual machines running on UML.

Article: http://www.virtual-strategy.com/article/articleview/1874/1/64/

MP3: http://virtual-strategy.com/podcasts/2007-02-13_UML_Linode.mp3

I’ll provide a transcript in the next few days for those that requested it.

-Chris

As a side note, Red Hat had approached me first about working for them before
Intel, so they are due some kudos as well, even though I ended up not accepting
their offer.

The other bit of news is that you won’t start seeing the this extra time kick
in until the end of July. Next week, I’m off to Iceland for some sightseeing,
and so I’ll be incommunicado.

Two weeks later, it’s KS/OLS time. Maybe I can get something done in the week
in between, but I’m not counting on too much. So, figure UML development on
my part will be pretty close to suspended until the last week of July.

Jeff ]]> http://blog.linode.com/2004/06/30/jeff-dike-now-fulltime-on-uml-development/feed/ 5 http://blog.linode.com/2004/05/28/request-for-testing-sysemu-performance-patches/ http://blog.linode.com/2004/05/28/request-for-testing-sysemu-performance-patches/#comments Fri, 28 May 2004 10:21:30 +0000 caker I’m looking for just a few Linode 64 users currently on hosts in the Fremont datacenter (host9 and up) to help test a new performance patch to the host and UML.

UML works by using ptrace, a function of Linux to intercept system calls made by applications. When your UML makes a system call, the host intercepts the call, performs the work inside UML, and null-ifies the system call on the host by converting that system call to “getpid” on the host. The problem with this is that it generates two context switches on the host.

With the sysemu patches on the host and in UML, it doesn’t bother running “getpid”, thereby reducing number of context switches from 2 to 1.

Here are some “real-world” benchmarks using Mysql’s run-all-tests script:

http://www.theshore.net/~caker/uml/sysemu-benchmarks.txt

In short, the tests ran 33% faster than they did without the sysemu patches.

[list][*] We’ll migrate you to host25, keeping your slot on the previous host reserved (in case we need to migrate you back). In case you’ve never migrated before, it’s an automated process which moves your filesystem images to the new host. No changes are required on your end, and downtime is limited to however long it takes to copy your images (usually less than 15 minutes or so for 3GB).
[*] Set your config profile to boot the 2.4.26-linode29-1um kernel
[*] Try to break things[/list]
If things go well for a few days, I’ll consider it stable and open up the server to the public. After another few weeks, we can move the other hosts to this kernel.

Secondly, this will help test 2.6.7-rc1 on the host, an upgrade from the current 2.6.4 kernel.

Thirdly, I would also like for some of you to test the 2.4.26-linode29-1um kernel, to make sure it still functions correctly on hosts without the sysemu patches. Please let me know your experience with this kernel. On non-sysemu enabled hosts, it should perform the same as the previous linode kernels.

Let me know if you’re interested…

Thanks!
-Chris

I would appreciate it if some of you would test a new option which changes the way UML writes to your filesystem files, and post your experiences here.

Normally, UML uses the standard open/close read/write library calls. The problem with this is that it duplicates data in the host’s page cache, and impacts over all disk i/o performance. The new option maps the filesystem file directly into the page cache, so it eliminates duplicate copies of pages and wasted page cache…

You’ll notice a new “Experimental Option” in the Edit Config Profile page. To turn it on, Enable ubd=mmap, save, and reboot. You should notice it in dmesg under kernel options. (dmesg | grep mmap)

Once we’ve had a bunch of successful reports, I’ll consider enabling this for everyone.

[color=darkred]WARNING:[/color][/size] I do NOT recommend just anyone turning this on yet. There is always a chance of data loss with a maturing feature such as this. Jeff Dike fixed the last known bug in ubd=mmap last month which ate filesystems over 4GB (so that would be a good test), so use this option with caution. There haven’t been any reports of mmap related failure on the UML mailing lists, but this isn’t a widely known option.

The current version (in the 2.4.24 kernels) has worked fine for me with mmap enabled, but your mileage may vary.

Thanks,
-Chris