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[Qemu-devel] ridiculously slow VM memory performance on Ryzen CPU
From: |
Qu Wenruo |
Subject: |
[Qemu-devel] ridiculously slow VM memory performance on Ryzen CPU |
Date: |
Wed, 25 Apr 2018 17:48:42 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
Hi,
When testing IO heavy work on my VM backed by Ryzen 1700 CPU, I turned
to brd modules, but surprisingly, the speed is even slower than some HDD:
---
$ sudo modprobe brd rd_nr=1 rd_size=1048576
$ dd if=/dev/zero of=/dev/ram0 bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 9.9928 s, 107 MB/s
---
107MB is pretty lame...
Even some HDD could be faster than this.
On host, it's much better:
---
$ if=/dev/zero of=/dev/ram0 bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 0.754641 s, 1.4 GB/s
---
For host hardware:
CPU: Ryzen 1700 All cores @ 3.8G
Mem: DDR4 2400 dual channel (8G x 2)
For host software:
Kernel: 4.16.3-1-ARCH
Qemu: 2.11.1-2
Distribution: Archlinux
VM setup is mostly default setup done by libvirt.
I'm not sure if this is related to this bug:
https://www.redhat.com/archives/vfio-users/2017-April/msg00019.html
Thanks,
Qu
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