Re: [Qemu-discuss] virtio-scsi really slow init with ArchLinux kernel

[Dongli Zhang]

Hi Chris,

On 07/12/2018 01:45 AM, Chris wrote:
> On Wed, Jul 11, 2018 at 12:43 PM, Greg Kurz <address@hidden> wrote:
>> I've been observing a similar delay on ppc64 with fedora28 guests:
>>
>> # dmesg | egrep 'scsi| sd '
>> [    1.530946] scsi host0: Virtio SCSI HBA
>> [    1.532452] scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    
>> 2.5+ PQ: 0 ANSI: 5
>> [   21.928378] sd 0:0:0:0: Power-on or device reset occurred
>> [   21.930012] sd 0:0:0:0: Attached scsi generic sg0 type 0
>> [   21.931554] sd 0:0:0:0: [sda] 83886080 512-byte logical blocks: (42.9 
>> GB/40.0 GiB)
>> [   21.931929] sd 0:0:0:0: [sda] Write Protect is off
>> [   21.933110] sd 0:0:0:0: [sda] Mode Sense: 63 00 00 08
>> [   21.934084] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, 
>> doesn't support DPO or FUA
>> [   21.943566] sd 0:0:0:0: [sda] Attached SCSI disk
>>
>> Kernel version is 4.16.16-300.fc28.ppc64. And I cannot reproduce the
>> issue with other distros that have an older kernel, eg, ubuntu 18.04
>> with kernel 4.15.0-23-generic.
>>
>> My first guess is that it might be a kernel-side regression introduced
>> in 4.16... maybe bisect ?
> 
> Interesting. I just tried kernel 4.17.5 from the mainline ppa on
> Ubuntu 18.04 and now there is a delay. It's only 7.5 seconds but still
> noticeable. There was previously no delay with the 4.15 kernel.

I did not observe any delay with stable 4.17.5 on ubuntu 18.04 (I built the
kernel myself with CONFIG_SCSI_VIRTIO=y):

# qemu-system-x86_64 -drive
file=/home/zhang/img/ubuntu1804.qcow2,format=qcow2,if=none,id=virt1 -device
virtio-scsi-pci,id=virt1 -device scsi-hd,drive=virt1 -m 4096M -enable-kvm -smp 6
-net nic -net user,hostfwd=tcp::5022-:22 -kernel
/home/zhang/test/linux-4.17.5/arch/x86_64/boot/bzImage -append "root=/dev/sda1
init=/sbin/init text" -enable-kvm


# uname -r
4.17.5

[0.190434] scsi host0: Virtio SCSI HBA
[0.190924] scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.5+ PQ: 0
ANSI: 5
[0.206282] random: fast init done
[0.216651] sd 0:0:0:0: Power-on or device reset occurred
[0.216907] sd 0:0:0:0: Attached scsi generic sg0 type 0
[0.217207] ata_piix 0000:00:01.1: version 2.13
[0.217613] sd 0:0:0:0: [sda] 62914560 512-byte logical blocks: (32.2 GB/30.0 
GiB)
[0.217959] sd 0:0:0:0: [sda] Write Protect is off
[0.218152] sd 0:0:0:0: [sda] Mode Sense: 63 00 00 08
[0.218193] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't
support DPO or FUA


In addition, I could not reproduce with '4.18-rc4' or 'v4.17-rc7'.


Dongli Zhang

> 
> Definitely seems like it could be something introduced in kernel 4.16.
> 
> Chris
>