Xen is a virtual machine monitor for x86 that supports execution of multiple guest operating systems. Xen-devel is the mailing list to ask questions and contribute to development. ()

Roger Pau Monné | 10 Feb 16:22

qemu-xen qdisk performance

Hello,

I've recently setup a Linux Dom0 with a 3.0.17 kernel and Xen 4.1.2,
and since the 3.x series doesn't have blktap support I'm using qdisk
to attach raw images. I've been playing with small images, something
like 1GB, and everything seemed fine, speed was not fantastic but it
was ok. Today I've set up a bigger machine, with a 20GB raw hdd and
the disk write throughput is really slow, inferior to 0.5MB/s. I'm
trying to install a Debian PV there, and after more than 3 hours it is
still installing the base system.

I've looked at the xenstore backend entries, and everything looks fine:

/local/domain/0/backend/qdisk/21/51712/frontend =
"/local/domain/21/device/vbd/51712"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/params =
"aio:/hdd/vm/servlet/servlet.img"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/frontend-id = "21"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/online = "1"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/removable = "0"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/bootable = "1"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/state = "4"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/dev = "xvda"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/type = "tap"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/mode = "w"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/feature-barrier = "1"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/info = "0"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/sector-size = "512"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/sectors = "40960000"   (n0,r21)
/local/domain/0/backend/qdisk/21/51712/hotplug-status = "connected"   (n0,r21)

(Continue reading)

Stefano Stabellini | 10 Feb 16:53

Re: qemu-xen qdisk performance

On Fri, 10 Feb 2012, Roger Pau Monné wrote:
> Hello,
> 
> I've recently setup a Linux Dom0 with a 3.0.17 kernel and Xen 4.1.2,
> and since the 3.x series doesn't have blktap support I'm using qdisk
> to attach raw images. I've been playing with small images, something
> like 1GB, and everything seemed fine, speed was not fantastic but it
> was ok. Today I've set up a bigger machine, with a 20GB raw hdd and
> the disk write throughput is really slow, inferior to 0.5MB/s. I'm
> trying to install a Debian PV there, and after more than 3 hours it is
> still installing the base system.
> 
> I've looked at the xenstore backend entries, and everything looks fine:
> 
> /local/domain/0/backend/qdisk/21/51712/frontend =
> "/local/domain/21/device/vbd/51712"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/params =
> "aio:/hdd/vm/servlet/servlet.img"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/frontend-id = "21"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/online = "1"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/removable = "0"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/bootable = "1"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/state = "4"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/dev = "xvda"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/type = "tap"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/mode = "w"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/feature-barrier = "1"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/info = "0"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/sector-size = "512"   (n0,r21)
> /local/domain/0/backend/qdisk/21/51712/sectors = "40960000"   (n0,r21)

(Continue reading)

Roger Pau Monné | 13 Feb 12:37

Re: qemu-xen qdisk performance

2012/2/10 Stefano Stabellini <stefano.stabellini <at> eu.citrix.com>:
> On Fri, 10 Feb 2012, Roger Pau Monné wrote:
>> Hello,
>>
>> I've recently setup a Linux Dom0 with a 3.0.17 kernel and Xen 4.1.2,
>> and since the 3.x series doesn't have blktap support I'm using qdisk
>> to attach raw images. I've been playing with small images, something
>> like 1GB, and everything seemed fine, speed was not fantastic but it
>> was ok. Today I've set up a bigger machine, with a 20GB raw hdd and
>> the disk write throughput is really slow, inferior to 0.5MB/s. I'm
>> trying to install a Debian PV there, and after more than 3 hours it is
>> still installing the base system.
>>
>> I've looked at the xenstore backend entries, and everything looks fine:
>>
>> /local/domain/0/backend/qdisk/21/51712/frontend =
>> "/local/domain/21/device/vbd/51712"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/params =
>> "aio:/hdd/vm/servlet/servlet.img"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/frontend-id = "21"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/online = "1"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/removable = "0"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/bootable = "1"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/state = "4"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/dev = "xvda"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/type = "tap"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/mode = "w"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/feature-barrier = "1"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/info = "0"   (n0,r21)
>> /local/domain/0/backend/qdisk/21/51712/sector-size = "512"   (n0,r21)

(Continue reading)

Stefano Stabellini | 13 Feb 12:59

Re: qemu-xen qdisk performance

On Mon, 13 Feb 2012, Roger Pau Monné wrote:
> > Yes, great improvements.
> > The old qemu-xen uses threads to simulate async IO so it is very slow;
> > upstream QEMU uses Linux AIO and is much faster.
> 
> That's great news, so qdisk performance in qemu-upstream should be
> similar to blktap?

Slightly better actually, from my very quick and dirty tests.

_______________________________________________
Xen-devel mailing list
Xen-devel <at> lists.xensource.com
http://lists.xensource.com/xen-devel

Roger Pau Monné | 13 Feb 15:41

Re: qemu-xen qdisk performance

2012/2/13 Stefano Stabellini <stefano.stabellini <at> eu.citrix.com>:
> On Mon, 13 Feb 2012, Roger Pau Monné wrote:
>> > Yes, great improvements.
>> > The old qemu-xen uses threads to simulate async IO so it is very slow;
>> > upstream QEMU uses Linux AIO and is much faster.
>>
>> That's great news, so qdisk performance in qemu-upstream should be
>> similar to blktap?
>
> Slightly better actually, from my very quick and dirty tests.

I'm sure blktap had some context switches (from kernel to userspace)
that qdisk doesn't have, since it's a pure userland implementation, so
it's plausible for it to be faster.

_______________________________________________
Xen-devel mailing list
Xen-devel <at> lists.xensource.com
http://lists.xensource.com/xen-devel

Return

Return to gmane.comp.emulators.xen.devel.

Project Web Page

Xen is a virtual machine monitor for x86 that supports execution of multiple guest operating systems. Xen-devel is the mailing list to ask questions and contribute to development. ()

Search Archive

Language

Change language

Options

Current view: Threads only / Showing only 20 lines / Not hiding cited text.
Change to All messages, whole messages, or hide cited text.

Post a message
NNTP Newsgroup
Classic Gmane web interface
XML

XML

RSS Feed
List Information

About Gmane