win10 installation - pathological slowness with i440fx ide cdrom

[RolandK]

does anybody have a clue, why booting up win10 from installation iso seems pathologically slow when using pc-i440fx instead of pc-q35 as machine type ?

can anybody confirm this observation ?

on my system , with q35 from power on to visibilty of the blue window boot logo, its' about 10 seconds whereas with i440fx, it's 1m45s until the blue bootlogo appears.

that quite a noticeably difference.

i did not observe any other significant performance difference (and also do not read that there is so big gap between those 2 machine types), but i always wondered about that long lag after power-on until the boot logo appears, so i decided to give a closer look on that

# diff -y 101.conf 102.conf
agent: 0                            agent: 0
boot: order=ide2                        boot: order=ide2
cores: 2                            cores: 2
cpu: host                            cpu: host
ide0: vms-qcow2:101/vm-101-disk-0.qcow2,backup=0,size=32G     |    ide0: vms-qcow2:102/vm-102-disk-0.qcow2,backup=0,size=32G
ide2: iso-images:iso/SW_DVD9_Win_Pro_10_22H2_64BIT_German_Pro    ide2: iso-images:iso/SW_DVD9_Win_Pro_10_22H2_64BIT_German_Pro
machine: pc-q35-8.0                          |    machine: pc-i440fx-8.0
memory: 4096                            memory: 4096
meta: creation-qemu=8.0.2,ctime=1687458558              |    meta: creation-qemu=8.0.2,ctime=1687458636
name: win10                              |    name: win10-2
numa: 0                                numa: 0
ostype: win10                            ostype: win10
scsihw: virtio-scsi-single                    scsihw: virtio-scsi-single
smbios1: uuid=bcc73a56-2d2b-4eac-8dc3-bbc26ce40f35          |    smbios1: uuid=951a505a-2e37-4d02-91dd-562396ee4d69
sockets: 1                            sockets: 1
vmgenid: 9dd29655-6d87-4388-abf9-472501aaf0f1              |    vmgenid: 08135549-538f-400d-a10d-bd4efa9583e2

 

[RolandK]

i have dig further.

with win 2022 server iso , i could see it's slow at the "loading files" stage and that brought me to the idea to try scsi instead if ide cdrom.

with scsi cdrom, the problem goes away completely. there is no noticeably difference anymore.

so the question is, why is ide cdrom performance so much worse and why is only i440fx affected ?

besides the question if this can be fixed for ide/i440fx - i see that ide cdrom is being mostly configured per default for all types of virtual machines.

why not use scsi instead as a default?

would it make sense to question ide cdrom default, when it performs that worse with i440fx ?

 

[RolandK]

i can reproduce that upstream on ubuntu 23.04 and have opened this bugticket

https://gitlab.com/qemu-project/qemu/-/issues/1731

 

[_gabriel]

confirmed here, qemu 7.2 + kernel 5.15
with Server 2019 , we can see the first "Loading files" part is too slow.
switching to q35 like I did by habits resolv this slowness booting

 

[Neobin]

For reference:
https://bugzilla.proxmox.com/show_bug.cgi?id=4805