Subject: Re: [PATCH vhost 0/7] vdpa/mlx5: Parallelize device suspend/resume

From: Leon Romanovsky <[email-masked]>
Date: Sun, 4 Aug 2024 11:48:39 +0300

On Fri, Aug 02, 2024 at 09:14:28AM -0400, Michael S. Tsirkin wrote:
> On Fri, Aug 02, 2024 at 10:20:17AM +0300, Dragos Tatulea wrote:
> > This series parallelizes the mlx5_vdpa device suspend and resume
> > operations through the firmware async API. The purpose is to reduce live
> > migration downtime.
> > 
> > The series starts with changing the VQ suspend and resume commands
> > to the async API. After that, the switch is made to issue multiple
> > commands of the same type in parallel.
> > 
> > Finally, a bonus improvement is thrown in: keep the notifierd enabled
> > during suspend but make it a NOP. Upon resume make sure that the link
> > state is forwarded. This shaves around 30ms per device constant time.
> > 
> > For 1 vDPA device x 32 VQs (16 VQPs), on a large VM (256 GB RAM, 32 CPUs
> > x 2 threads per core), the improvements are:
> > 
> > +-------------------+--------+--------+-----------+
> > | operation         | Before | After  | Reduction |
> > |-------------------+--------+--------+-----------|
> > | mlx5_vdpa_suspend | 37 ms  | 2.5 ms |     14x   |
> > | mlx5_vdpa_resume  | 16 ms  | 5 ms   |      3x   |
> > +-------------------+--------+--------+-----------+
> > 
> > Note for the maintainers:
> > The first patch contains changes for mlx5_core. This must be applied
> > into the mlx5-vhost tree [0] first. Once this patch is applied on
> > mlx5-vhost, the change has to be pulled from mlx5-vdpa into the vhost
> > tree and only then the remaining patches can be applied.
> 
> Or maintainer just acks it and I apply directly.

We can do it, but there is a potential to create a conflict between your tree
and netdev for whole cycle, which will be a bit annoying. Easiest way to avoid
this is to have a shared branch, but in august everyone is on vacation, so it
will be probably fine to apply such patch directly.

Thanks

> 
> Let me know when all this can happen.
> 
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/mellanox/linux.git/log/?h=mlx5-vhost
> > 
> > Dragos Tatulea (7):
> >   net/mlx5: Support throttled commands from async API
> >   vdpa/mlx5: Introduce error logging function
> >   vdpa/mlx5: Use async API for vq query command
> >   vdpa/mlx5: Use async API for vq modify commands
> >   vdpa/mlx5: Parallelize device suspend
> >   vdpa/mlx5: Parallelize device resume
> >   vdpa/mlx5: Keep notifiers during suspend but ignore
> > 
> >  drivers/net/ethernet/mellanox/mlx5/core/cmd.c |  21 +-
> >  drivers/vdpa/mlx5/core/mlx5_vdpa.h            |   7 +
> >  drivers/vdpa/mlx5/net/mlx5_vnet.c             | 435 +++++++++++++-----
> >  3 files changed, 333 insertions(+), 130 deletions(-)
> > 
> > -- 
> > 2.45.2
> 
>