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[Qemu-discuss] virtio-console downgrade the virtio-pci-blk performance

From: Feng Li
Subject: [Qemu-discuss] virtio-console downgrade the virtio-pci-blk performance
Date: Sun, 30 Sep 2018 13:25:58 +0800

I found an obvious performance downgrade when virtio-console combined
with virtio-pci-blk.

This phenomenon exists in nearly all Qemu versions and all Linux
(CentOS7, Fedora 28, Ubuntu 18.04) distros.

This is a disk cmd:

If I add "-device
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5  ", the virtio
disk 4k iops (randread/randwrite) would downgrade from 60k to 40k.

In VM, if I rmmod virtio-console, the performance will back to normal.

Any idea about this issue?

I don't know this is a qemu issue or kernel issue.

Thanks in advance.
Thanks and Best Regards,

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