Re: Slower transfers on XEN

["Marcin M. Jessa" <lists%yazzy.org@localhost>]

On 03/17/2010 01:19 AM, Greg Troxel wrote:
> "Marcin M. Jessa" <lists%yazzy.org@localhost> writes:
>
>   
> > I have an AMD64 server running NetBSD 5.0.2 with two 500Gb IDE drives.
> > The drives are raided with RaidFrame and Raid 1. The FFS file systems
> > are mounted with log option.
> > Copying large files i noticed I get about 6-7 mbit/s when running Xen
> > and about 10-11 when running GENERIC kernel and scping to the same
> > file system.
> > I had to disable ACPI on this server as well.
> > Any idea why there is this dicrease in performance ?
> >     
>
> My experience was
>
>   RAID1 (raidframe) for dom0 fs
>   UFS2 fs for backing files
>   files created with dd (zero-filled, non-sparse)
>
> I remember dimly
>
>   70 MB/s read from raw raid device
>   ~10% less read from file on dom0
>   ~10% less than that read from 'raw device' on domU (rxbd0d)
>
> so your 6-7 vs 10-11 seems like too much.  try the above 3 tests and
> post the real numbers.
>   
Disabling ACPI and APIC in kernel improved transfer speed over ftp and 
scp with 70-80%.
Why is this happening ?


Marcin

P.S My observations match your, transfer speed is ~10% less than with 
kernel without XEN,
but I can live with that.