Xen DomU poor I/O performance

classic Classic list List threaded Threaded
2 messages Options
Reply | Threaded
Open this post in threaded view
|

Xen DomU poor I/O performance

Michał Chybowski
Hi

I'm working on SR for Xen using independent iSCSI targets for each VDI
via IPoIB on Mellanox Technologies MT25208 [InfiniHost III Ex] (rev 20).

VDI is correctly attaching, detaching, etc. but it's I/O is terrible.
VDI is attached to VM without use of blktap as with high I/O from VMs it
can almost completely use up whole Dom0's CPU.

Using fio in DomU with --fsync=1 gives me exactly 0 IOPS.
If at the same time I'll run `ioping -D -i 0.01 filename` - fio shows I/O.
If I'll run `ping -f <ip of iSCSI target>`, I/O also "starts" to show up.
Also if I use dd with --oflag=dsync, I/O looks like above.

The same behaviour occurs when using classic 1Gbit/s Ethernet.

This does not happen if I log in the target in Dom0 and try the same
tests with the same parameters there or if I'm using blktap (both on
IPoIB and Ethernet).

Is there any method of finding source of this behaviour?

--
Regards
M


_______________________________________________
Xen-users mailing list
[hidden email]
https://lists.xen.org/xen-users
Reply | Threaded
Open this post in threaded view
|

Re: Xen DomU poor I/O performance

George Dunlap-5
On Mon, Oct 9, 2017 at 11:56 AM, Michał Chybowski
<[hidden email]> wrote:
> Hi
>
> I'm working on SR for Xen using independent iSCSI targets for each VDI via
> IPoIB on Mellanox Technologies MT25208 [InfiniHost III Ex] (rev 20).
>
> VDI is correctly attaching, detaching, etc. but it's I/O is terrible. VDI is
> attached to VM without use of blktap as with high I/O from VMs it can almost
> completely use up whole Dom0's CPU.

By using the terms 'SR' and 'VDI', I assume you're talking about using
XenServer (or OpenXenServer)?

This mailing list is for supporting the core hypervisor toolstack (xl
and libvirt).  For XenServer / xapi support you'll have to go to a
XenServer-specific forum.

 -George

_______________________________________________
Xen-users mailing list
[hidden email]
https://lists.xen.org/xen-users