Re: Elvis upstreaming plan

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

On Sun, Nov 24, 2013 at 11:22:17AM +0200, Razya Ladelsky wrote:
> Hi all,
> 
> I am Razya Ladelsky, I work at IBM Haifa virtualization team, which 
> developed Elvis, presented by Abel Gordon at the last KVM forum: 
> ELVIS video:  https://www.youtube.com/watch?v=9EyweibHfEs 
> ELVIS slides: https://drive.google.com/file/d/0BzyAwvVlQckeQmpnOHM5SnB5UVE 
> 
> 
> According to the discussions that took place at the forum, upstreaming 
> some of the Elvis approaches seems to be a good idea, which we would like 
> to pursue.
> 
> Our plan for the first patches is the following: 
> 
> 1.Shared vhost thread between mutiple devices 
> This patch creates a worker thread and worker queue shared across multiple 
> virtio devices 
> We would like to modify the patch posted in
> https://github.com/abelg/virtual_io_acceleration/commit/3dc6a3ce7bcbe87363c2df8a6b6fee0c14615766 
> to limit a vhost thread to serve multiple devices only if they belong to 
> the same VM as Paolo suggested to avoid isolation or cgroups concerns.
> 
> Another modification is related to the creation and removal of vhost 
> threads, which will be discussed next.
>
> 2. Sysfs mechanism to add and remove vhost threads 
> This patch allows us to add and remove vhost threads dynamically.
> 
> A simpler way to control the creation of vhost threads is statically 
> determining the maximum number of virtio devices per worker via a kernel 
> module parameter (which is the way the previously mentioned patch is 
> currently implemented)
> 
> I'd like to ask for advice here about the more preferable way to go:
> Although having the sysfs mechanism provides more flexibility, it may be a 
> good idea to start with a simple static parameter, and have the first 
> patches as simple as possible. What do you think?
> 
> 3.Add virtqueue polling mode to vhost 
> Have the vhost thread poll the virtqueues with high I/O rate for new 
> buffers , and avoid asking the guest to kick us.
> https://github.com/abelg/virtual_io_acceleration/commit/26616133fafb7855cc80fac070b0572fd1aaf5d0
> 
> 4. vhost statistics
> This patch introduces a set of statistics to monitor different performance 
> metrics of vhost and our polling and I/O scheduling mechanisms. The 
> statistics are exposed using debugfs and can be easily displayed with a 
> Python script (vhost_stat, based on the old kvm_stats)
> https://github.com/abelg/virtual_io_acceleration/commit/ac14206ea56939ecc3608dc5f978b86fa322e7b0
> 
> 
> 5. Add heuristics to improve I/O scheduling 
> This patch enhances the round-robin mechanism with a set of heuristics to 
> decide when to leave a virtqueue and proceed to the next.
> https://github.com/abelg/virtual_io_acceleration/commit/f6a4f1a5d6b82dc754e8af8af327b8d0f043dc4d
> 
> This patch improves the handling of the requests by the vhost thread, but 
> could perhaps be delayed to a 
> later time , and not submitted as one of the first Elvis patches.
> I'd love to hear some comments about whether this patch needs to be part 
> of the first submission.
> 
> Any other feedback on this plan will be appreciated,
> Thank you,
> Razya


How about we start with the stats patch?
This will make it easier to evaluate the other patches.