[Xen-users] Big I/O performance difference between dom0 and domU

[Marcin Owsiany <marcin@xxxxxxxxxx>]

Hi,

I am setting up a dual CPU PowerEdge 2550 system with PERC 3Di
controller (aacraid) with 3 18GB disks in RAID5 and XEN 3.0.3-0-2,
credit scheduler, PAE (the Debian package in etch). This is not best
hardware, but what worries me more is the poor I/O performance in domU
compared to dom0.

With both domains having 500 MB of RAM, testing with bonnie++ on the
same 5GB LVM volume with xfs filesystem, with 4GB test data size, I'm
getting:

-----+-------------------+--------------------+-----------------------
Test | block read [kB/s] | block write [kB/s] | random seeks [/sec]
-----+-------------------+--------------------+-----------------------
dom0 | 10308             | 64806              | 325.3
domU |  7299             | 53469              | 265.6
-----+-------------------+--------------------+-----------------------
~drop|    30%            |    17%             |  18%
-----+-------------------+--------------------+-----------------------

The results are basically the same whether I use the default vcpu
arrangement (2 vcpus for dom0, one for domU) or set it to one vcpu per
domain, each pinned to a different physical cpu.

Any suggestions are welcome...


-- 
Marcin Owsiany <marcin@xxxxxxxxxx>              http://marcin.owsiany.pl/
GnuPG: 1024D/60F41216  FE67 DA2D 0ACA FC5E 3F75  D6F6 3A0D 8AA0 60F4 1216
 
"Every program in development at MIT expands until it can read mail."
                                                              -- Unknown

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