Re: [PATCH 0/2 v2] Flexible proportions for BDIs

[Fengguang Wu <fengguang.wu@intel.com>]

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> > > Look at the gray "bdi setpoint" lines. The
> > > VM_COMPLETIONS_PERIOD_LEN=8s kernel is able to achieve roughly the
> > > same stable bdi_setpoint as the vanilla kernel, while being able to
> > > adapt to the balanced bdi_setpoint much more fast (actually now the
> > > bdi_setpoint is immediately close to the balanced value when
> > > balance_dirty_pages() starts throttling, while the vanilla kernel
> > > takes about 20 seconds for bdi_setpoint to grow up).
> >   Which graph is from which kernel? All four graphs have the same name so
> > I'm not sure...
> 
> They are for test cases:
> 
> 0.5s period
>         bay/JBOD-2HDD-thresh=1000M/xfs-1dd-1-3.4.0-rc2-prop+/balance_dirty_pages-pages+.png
> 3s period
>         bay/JBOD-2HDD-thresh=1000M/xfs-1dd-1-3.4.0-rc2-prop3+/balance_dirty_pages-pages+.png
> 8s period
>         bay/JBOD-2HDD-thresh=1000M/xfs-1dd-1-3.4.0-rc2-prop8+/balance_dirty_pages-pages+.png
> vanilla
>         bay/JBOD-2HDD-thresh=1000M/xfs-1dd-1-3.3.0/balance_dirty_pages-pages+.png
> 
> >   The faster (almost immediate) initial adaptation to bdi's writeout fraction
> > is mostly an effect of better normalization with my patches. Although it is
> > pleasant, it happens just at the moment when there is a small number of
> > periods with non-zero number of events. So more important for practice is
> > in my opininion to compare transition of computed fractions when workload
> > changes (i.e. we start writing to one bdi while writing to another bdi or
> > so).
> 
> OK. I'll test this scheme and report back.
> 
>         loop {
>                 dd to disk 1 for 30s
>                 dd to disk 2 for 30s
>         }

Here are the new results. For simplicity I run the dd dirtiers
continuously, and start another dd reader to knock down the write
bandwidth from time to time:

         loop {
                 dd from disk 1 for 30s
                 dd from disk 2 for 30s
         }

The first attached iostat graph shows the resulting read/write
bandwidth for one of the two disks.

The followed graphs are for
        - 3s period
        - 8s period
        - vanilla
in order. The test case is (xfs-1dd, mem=2GB, 2 disks JBOD).

Thanks,
Fengguang

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