[vfio-users] Stutter in games

[Alex Williamson]

On Mon, Jan 23, 2017 at 12:50 PM, Laszlo Ersek <lersek at redhat.com> wrote:

> On 01/23/17 20:02, Alex Williamson wrote:
>
> > isolcpus
> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/
> linux.git/tree/Documentation/admin-guide/kernel-parameters.txt#n1669
>
> BTW, do you know a method to massage isolcpus without a host reboot? The
> last paragraph of the linked section doesn't look promising ("... can
> cause problems and suboptimal load balancer performance").
>
> Sometimes the same host is temporarily dedicated to run a VM where
> latency doesn't matter much, but throughput does (example: distcc server
> with assigned 1Gbit NIC VF); and sometimes the host is dedicated to a VM
> where isolcpus would be beneficial to latency (example: interactive 3D
> stuff with assigned GPU).
>
> It's quite a pain to reboot the host just to switch between these two;
> that sort of eliminates the benefits of virtualization. Furthermore,
>
> - the LUKS password for the host needs to be entered again,
> - startup of guests with bridged virtual NICs has to await host DHCP for
> internet connectivity again,
> - for remote management with virt-manager, the multiplexing SSH master
> process on the client has to be re-launched (and then virt-manager has
> to be reconnected over the local muxer socket),
> - etc
>

No need to sell me on it, I agree it'd be useful.  I imagine there's some
way to do this with cgroups, ie. dynamically add/remove cpus from the
default init process cpuset, but it hasn't nagged at me enough to find time
to investigate further.  It seems like someone had reported a more dynamic
setup.  Thanks,

Alex
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