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kern/50604: ld(4) on top of virtio(4) performs very badly
>Number: 50604
>Category: kern
>Synopsis: ld(4) on top of virtio(4) performs very badly
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: kern-bug-people
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Fri Jan 01 19:40:00 +0000 2016
>Originator: tron%zhadum.org.uk@localhost
>Release: NetBSD 7.99.25 2016-01-01 sources
>Organization:
Matthias Scheler https://zhadum.org.uk/
>Environment:
System: NetBSD lyssa.zhadum.org.uk 7.99.25 NetBSD 7.99.25 (GENERIC) #0: Fri Jan 1 15:28:41 GMT 2016 tron%lyssa.zhadum.org.uk@localhost:/src/sys/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
I've got a NetBSD-current virtual machine running as a KVM guest.
The host is a Debian 8.2 system (Linux kernel 3.16.0, QEMU 2.1).
Today I tried to switch on all of the virtual machine's three disks from
"IDE" to "VirtIO" to improve performance. But to my big surprise I got
a massive performance degradation instead. I've used un-tar-ring the
Perl 5.22.1 sources as a crude benchmark. Here are the results:
IDE: 1.67s user 0.83s system 50% cpu 4.935 total
VirtIO: 1.74s user 0.75s system 2% cpu 1:27.43 total
It seems that virtio(4) is twenty times slower. As I've never experienced
similar problems with Linux guests (at work) I guess that this is a problem
with NetBSD's virtio(4) driver.
>How-To-Repeat:
cd /some/filesystem/on/ld/at/virtio
time sh -c "tar xzf /usr/pkgsrc/distfiles/perl-5.22.1.tar.bz2; sync"
>Fix:
Not known
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