File System Performance - 10x slower

File System Performance - 10x slower

[Nauzad Sadry]

Hello all

I am evaluating File I/O performance using Xen & comparing it with
baseline (Fedora Core 3, with 2.6.9 kernel).

Here are the commands that I use for I/O
write I/O:  dd if=/dev/zero of=file1 bs=4K count=256K
read I/O:  dd of=/dev/null if=file1 bs=4K count=256K

Here are some numbers (all test results are reported in MB/second)

Read I/O
- Baseline Fedora Core 3                  - 32
- XEN domain 0                               -  9.3
- XEN domain 1                               - 2.3 

Write I/O
- Baseline Fedora Core 3                  - 22
- XEN domain 0                               -  9.8
- XEN domain 1                               - 2.5 

- Dom0 (without starting xend) results in 2x slower performance
- DomU results in 9-10x slower performance 

I get similar results for domain-1 using both File-based & LVM-based VBD

Can someone why I am getting such huge difference in performance
compared to baseline ??

Thanks

Nauzad


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Re: File System Performance - 10x slower

[Steven Hand]

> I am evaluating File I/O performance using Xen & comparing it with
> baseline (Fedora Core 3, with 2.6.9 kernel).
>
[snip poor I/O results]
>
> Can someone why I am getting such huge difference in performance
> compared to baseline ??

What version of Xen are you using? 2.0.x [preferably 2.0.3]? 

Did you move /lib/tls out of the way on the various root filesystems? 

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). 


Can you post the output of Xen / dom0 / domU booting, and your
configuration files? 


cheers,

S.




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RE: File System Performance - 10x slower

[Ian Pratt]

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 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). 

Ian


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RE: File System Performance - 10x slower

[Leigh Brown]

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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Re: File System Performance - 10x slower

[Nauzad Sadry]

Thanks guys for your help

I will inspect the driver configuration in my system & get back.

On using hdparm is found out that DMA is disabled by default in Xen
(it was enabled on baseline) & I probably need to rebulid the kernel
with this option turned on.

If there are any other ways to turn on this option, please let me know

Thanks

Nauzad

On Tue, 11 Jan 2005 19:11:53 -0000, Ian Pratt <m+Ian.Pratt@cl.cam.ac.uk> wrote:
> 
> 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 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).
> 
> Ian
>


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Re: File System Performance - 10x slower

[Jan Kundrát]

Nauzad Sadry wrote:
> On using hdparm is found out that DMA is disabled by default in Xen
> (it was enabled on baseline) & I probably need to rebulid the kernel
> with this option turned on.
> 
> If there are any other ways to turn on this option, please let me know

as Ian already said, you'll have to include your IDE chipset's driver 
into kernel. It is located under Device drivers->ATA/ATAPI/MFM/RLL support.

-jkt

-- 
cd /local/pub && more beer > /dev/mouth



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Re: File System Performance - 10x slower

[Nauzad Sadry]

Hello folks

On turning DMA on in XEN kernel I managed to achieve file i/o
performance comparable to baseline

Thanks for your help

Nauzad


On Tue, 11 Jan 2005 23:15:55 +0100, Jan Kundrát <jan.kundrat@fzu.cz> wrote:
> Nauzad Sadry wrote:
> > On using hdparm is found out that DMA is disabled by default in Xen
> > (it was enabled on baseline) & I probably need to rebulid the kernel
> > with this option turned on.
> >
> > If there are any other ways to turn on this option, please let me know
> 
> as Ian already said, you'll have to include your IDE chipset's driver
> into kernel. It is located under Device drivers->ATA/ATAPI/MFM/RLL support.
> 
> -jkt
> 
> --
> cd /local/pub && more beer > /dev/mouth
> 
>


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