dm-ioband + bio-cgroup benchmarks

[Hirokazu Takahashi]

Hi,

> > > > > > I have got excellent results of dm-ioband, that controls the disk I/O
> > > > > > bandwidth even when it accepts delayed write requests.
> > > > > > 
> > > > > > In this time, I ran some benchmarks with a high-end storage. The
> > > > > > reason was to avoid a performance bottleneck due to mechanical factors
> > > > > > such as seek time.
> > > > > > 
> > > > > > You can see the details of the benchmarks at:
> > > > > > http://people.valinux.co.jp/~ryov/dm-ioband/hps/
> > > > 
> > > >   (snip)
> > > > 
> > > > > Secondly, why do we have to create an additional dm-ioband device for 
> > > > > every device we want to control using rules. This looks little odd
> > > > > atleast to me. Can't we keep it in line with rest of the controllers
> > > > > where task grouping takes place using cgroup and rules are specified in
> > > > > cgroup itself (The way Andrea Righi does for io-throttling patches)?
> > > > 
> > > > It isn't essential dm-band is implemented as one of the device-mappers.
> > > > I've been also considering that this algorithm itself can be implemented
> > > > in the block layer directly.
> > > > 
> > > > Although, the current implementation has merits. It is flexible.
> > > >   - Dm-ioband can be place anywhere you like, which may be right before
> > > >     the I/O schedulers or may be placed on top of LVM devices.
> > > 
> > > Hi,
> > > 
> > > An rb-tree per request queue also should be able to give us this
> > > flexibility. Because logic is implemented per request queue, rules can be 
> > > placed at any layer. Either at bottom most layer where requests are
> > > passed to elevator or at higher layer where requests will be passed to 
> > > lower level block devices in the stack. Just that we shall have to do
> > > modifications to some of the higher level dm/md drivers to make use of
> > > queuing cgroup requests and releasing cgroup requests to lower layers.
> > 
> > Request descriptors are allocated just right before passing I/O requests
> > to the elevators. Even if you move the descriptor allocation point
> > before calling the dm/md drivers, the drivers can't make use of them.
> > 
> 
> You are right. request descriptors are currently allocated at bottom
> most layer. Anyway, in the rb-tree, we put bio cgroups as logical elements
> and every bio cgroup then contains the list of either bios or requeust
> descriptors. So what kind of list bio-cgroup maintains can depend on
> whether it is a higher layer driver (will maintain bios) or a lower layer
> driver (will maintain list of request descriptors per bio-cgroup).

I'm getting confused about your idea.

I thought you wanted to make each cgroup have its own rb-tree,
and wanted to make all the layers share the same rb-tree.
If so, are you going to put different things into the same tree?
Do you even want all the I/O schedlers use the same tree?

Are you going to block request descriptors in the tree?