RE: [Xen-devel] File System Performance - 10x slower

["Leigh Brown" <leigh@xxxxxxxxxxxxx>]

Ian Pratt said:
>> I ask since it should be almost *impossible* to get anything more
>> than a very small % slowdown on disk I/O unless things are very
>> broken -- most of our benchmarks to date show 0% slowdown (and
>> in some cases involving domU, a speedup due to additional buffering).
>
> Check that the domain 0 kernel you are using has the appropriate drivers
> for your hardware. It's probably using PIO or something daft.

I had exactly this problem because the drivers for various IDE chipsets
are missing in the default xen0 config.  When I added the VIA 82cxxx
driver back into the config, performance returned to normal (i.e. went
from ~4MB/sec to ~38MB/sec in hdparm).

It might be worth enabling the various IDE drivers in the standard
configuration as I also tripped up over the fact the PDC 202xx driver
was missing when I tried Xen on another machine.  It wouldn't boot
until I used a xen0 kernel with that driver included.

Regards,

Leigh.



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