Hi,

Aside from the big improvements in the 1G,100M,10M cases, the
thresh=1M cases show big regressions. But there is a good reason.

      3.1.0-rc8-vanilla+        3.1.0-rc8-nfs-wq4+
------------------------  ------------------------
                   21.85       +97.9%        43.23  NFS-thresh=100M/nfs-10dd-4k-32p-32768M-100M:10-X
                   51.38       +42.6%        73.26  NFS-thresh=100M/nfs-1dd-4k-32p-32768M-100M:10-X
                   28.81      +145.3%        70.68  NFS-thresh=100M/nfs-2dd-4k-32p-32768M-100M:10-X
                   13.74       +57.1%        21.59  NFS-thresh=10M/nfs-10dd-4k-32p-32768M-10M:10-X
                   29.11        -0.3%        29.02  NFS-thresh=10M/nfs-1dd-4k-32p-32768M-10M:10-X
                   16.68       +90.5%        31.78  NFS-thresh=10M/nfs-2dd-4k-32p-32768M-10M:10-X
                   48.88       +41.2%        69.01  NFS-thresh=1G/nfs-10dd-4k-32p-32768M-1024M:10-X
                   57.85       +32.7%        76.74  NFS-thresh=1G/nfs-1dd-4k-32p-32768M-1024M:10-X
                   47.13       +63.1%        76.87  NFS-thresh=1G/nfs-2dd-4k-32p-32768M-1024M:10-X
                    9.82       -33.0%         6.58  NFS-thresh=1M/nfs-10dd-4k-32p-32768M-1M:10-X
                   13.72       -18.1%        11.24  NFS-thresh=1M/nfs-1dd-4k-32p-32768M-1M:10-X
                   15.68       -65.0%         5.48  NFS-thresh=1M/nfs-2dd-4k-32p-32768M-1M:10-X
                  354.65       +45.4%       515.48  TOTAL write_bw

The regressions in the thresh=1M cases are reasonably caused by the
much reduced dirty/writeback/unstable pages.

The attached graphs for the NFS-thresh=1M/nfs-10dd cases show the
differences. The vanilla kernel (first graph) is much more permissive
to allow dirty pages to exceed the global dirty limit, while the
IO-less one applies the global dirty limit much more rigidly.

Given the 18MB vs. 3MB max dirty+writeback+unstable pages, it's not
surprising to see the better performance in the vanilla kernel. And
it does not mean anything inherently wrong in the IO-less logic.

Thanks,
Fengguang