RE: [Xen-users] domains gets stalled for N seconds

["Damjan Pipan" <damjan.pipan@xxxxxxx>]

Hi,

Can somebody explain me if there are any issues with high IO ( a lot of DMA 
requests) usage and Xen?

Is it possible that two domains starve each other and then one gets stalled?

Is the pdf below relevant?

Damjan Pipan  

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Damjan Pipan
Sent: Tuesday, October 14, 2008 1:49 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] domains gets stalled for N seconds

Hi,

we have a software accessing a lot of small files. We installed Xen 3.2 on a 
server with two quad core Xeons. We installed two
domains with our software on Linux and put it into production.

The problem is that I suspect that domains are not running at full (hardware) 
speed and they are getting stalled from time to time.
I can see a lot of wait in top and "top -d .5" gets stalled also from time to 
time for some seconds (cca 5s)

I found discussion that using the current implementation of IO handling can 
lead to huge delays - up to 30 seconds. 
http://xen.org/files/xensummit_fall07/13_ScottRixner.pdf



xen-de:~# xm info
host                   : xen-de
release                : 2.6.18.8-xen
version                : #2 SMP Fri Jun 27 21:27:02 UTC 2008
machine                : x86_64
nr_cpus                : 8
nr_nodes               : 1
cores_per_socket       : 4
threads_per_core       : 1
cpu_mhz                : 3000
hw_caps                : 
bfebfbff:20100800:00000000:00000140:000ce3bd:00000000:00000001
total_memory           : 16382
free_memory            : 4
node_to_cpu            : node0:0-7
xen_major              : 3
xen_minor              : 2
xen_extra              : .1
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          : unavailable
cc_compiler            : gcc version 4.1.2 20061115 (prerelease) (Debian 
4.1.1-21)
cc_compile_by          : root
cc_compile_domain      : xlab.si
cc_compile_date        : Fri Jun 27 23:35:01 CEST 2008
xend_config_format     : 4

Could you point me how to improve IO performance?

Damjan


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