[Xen-users] Disk performance on guest incredibly low.

[<frm@xxxxxxxxxxx>]

My disk performance of Xen guest is very slow. My latest configuration:

At guest, I have:

`    dd if=/dev/zero of=a_file bs=1M count=1024 conv=fsync oflag=direct
    1024+0 records in
    1024+0 records out
    1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.6421 s, 68.6 MB/s
`

At Dom0 I have:

`    dd if=/dev/zero of=a_file bs=1M count=1024 conv=fsync oflag=direct
    1024+0 records in
    1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 3.81855 s, 281 MB/s
`

The dom0 is about 5 times faster than the guest.

Data about the hypervisor
`    Xen version 4.11.1 
Boot parameters:
    options=loglvl=all noreboot dom0_mem=2048M max=2048M dom0_max_vcpus=4
dom0_vcpus_pin iommu=verbose ucode=scan flask=disabled conring_size=2097152
    kernel=vmlinuz-4.18.0-0.bpo.1-amd64 root=/dev/mapper/nuc1-root ro
console=tty quiet splash vt.handoff=7
    ramdisk=initrd.img-4.18.0-0.bpo.1-amd64
`

config file guest:

`    bootloader = '/usr/local/bin/pygrub'
    extra="console=hvc0"
    vcpus       = '4'
    memory      = '8192'
    root        = '/dev/xvda1 ro'
    disk        = [
                  'phy:/dev/vm/compute-root,xvda1,w'
              ]
    type      = 'pvh'
`

Startup parameters guest:

`    root=/dev/xvda1 ro elevator=noop xen_blkfront.max_indirect_segments=256
root=/dev/xvda1 ro console=hvc0
`


If I have tried also hvm and pv virtualisation modes; not improvement.

Any ideas?


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