Re: hdd kills vm
Greetings Martin,
Sent: Sunday, October 22, 2023 at 12:37 PM
From: "Martin Kletzander" <mkletzan(a)redhat.com>
To: "daggs" <daggs(a)gmx.com>
Cc: libvir-list(a)redhat.com
Subject: Re: hdd kills vm
On Fri, Oct 20, 2023 at 02:42:38PM +0200, daggs wrote:
>Greetings,
>
>I have a windows 11 vm running on my Gentoo using libvirt (9.8.0) + qemu (8.1.2),
I'm passing almost all available resources to the vm
>(all 16 cpus, 31 out of 32 GB, nVidia gpu is pt), but the performance is not good,
system lags, takes long time to boot.
There are couple of things that stand out to me in your setup and I'll
assume the host has one NUMA node with 8 cores, each with 2 threads as,
just like you set it up in the guest XML.
thats correct, see:
$ lscpu | grep -i numa
NUMA node(s): 1
NUMA node0 CPU(s): 0-15
however:
$ dmesg | grep -i numa
[ 0.003783] No NUMA configuration found
can that be the reason?
* When you give the guest all the CPUs the host has there is nothing
left to run the host tasks. You might think that there "isn't
anything running", but there is, if only your init system, the kernel
and the QEMU which is emulating the guest. This is definitely one of
the bottlenecks.
I've tried with 12 out of 16, same behavior.
* The pinning of vCPUs to CPUs is half-suspicious. If you are trying to
make vCPU 0 and 1 be threads on the same core and on the host the
threads are represented as CPUs 0 and 8, then that's fine. If that is
just copy-pasted from somewhere, then it might not reflect the current
situation and can be source of many scheduling issues (even once the
above is dealt with).
I found a site that does it for you, if it is wrong, can
you point me to a place I can read about it?
* I also seem to recall that Windows had some issues with systems that
have too many cores. I'm not sure whether that was an issue with an
edition difference or just with some older versions, or if it just did
not show up in the task manager, but there was something that was
fixed by using either more sockets or cores in the topology. This is
probably not the issue for you though.
>after trying a few ways to fix it, I've concluded that the issue might be related
to the why the hdd is defined at the vm level.
>here is the xml: https://bpa.st/MYTA
>I assume that the hdd sits on the sata ctrl causing the issue but I'm not sure
what is the proper way to fix it, any ideas?
>
It looks like your disk is on SATA, but I don't see why that would be an
issue. Passing the block device to QEMU as VirtIO shouldn't cause that
much of a difference. Try measuring the speed of the disk on the host
and then in the VM maybe. Is that SSD or NVMe? I presume that's not
spinning rust, is it.
as seen, I have 3 drives, 2 cdroms as sata and one hdd pt as
virtio, I read somewhere that if the controller of the virtio
device is sata, than it doesn't uses the virtio optimally.
it is a spindle, nvmes are too expensive where I live, frankly, I don't need lightning
fast boot, the other BM machines running windows on spindle
run it quite fast and they aren't half as fast as this server
>Thanks,
>
>Dagg.
>