Re: [Qemu-devel] [PATCH] virtio: improve virtio devices initialization time

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jan 12, 2018 at 10:48:21AM +0200, Gal Hammer wrote:
> 
> On Thu, Jan 11, 2018 at 9:52 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> 
>     On Thu, Jan 11, 2018 at 12:16:56PM +0200, Gal Hammer wrote:
>     > The loading time of a VM is quite significant when its virtio
>     > devices uses a large amount of virt-queues (e.g. a virtio-serial
>     > device with
>     ​​
>     max_ports=511). Most of the time is spend in the
>     > creation of all the required event notifiers (ioeventfd and memory
>     > regions).
>     >
>     > This patch pack all the changes to the memory regions in a
>     > single memory transaction.
>     >
>     > Reported-by: Sitong Liu <siliu@redhat.com>
>     > Reported-by: Xiaoling Gao <xiagao@redhat.com>
>     > Signed-off-by: Gal Hammer <ghammer@redhat.com>
> 
>     Nice patch! Any timing numbers to share before/after?
> 
> 
> Thanks. Unfortunately I made a mistake in the shutdown code (the transaction
> is wrapping the code which doesn't modify the memory regions), so a V2 is on
> its way.
> 
> As for the timing. Running a VM with 25 virtio-serial devices,​ each one with
> max_ports=511, results in a boot time of around 30 minutes. With this patch
> (and a another patch to kvm) reduce it to approximately 3 minutes.

Good to know, sounds like an important fix to have.
Since you plan to do v2 anyway, please add this info
in the commit log.


> This was reported and tracked here: https://bugzilla.redhat.com/show_bug.cgi?id
> =1528588
> 
>     Gal.