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> I could reproduce this very well on a random OS image that I had around.
>  This is raw over XFS over dm-crypt, and the image is about 75% sparse
> (8.2G used over 35G).  I only get 1-2%, but still it's visible.
> 
> However I can hardly reproduce it when using a partition directly:
> 
>          old    new
> mean     9.9565 9.9636      (+0.07%)
> stddev   0.0405 0.0537
> min      9.871  9.867
> median   9.973  9.971
> max      10.01  10.053
> count    20     20
> 
> I haven't tried removing layers (e.g. fully-allocated XFS image without
> dm-crypt).

Could not reproduce it with a fully-allocated XFS image, on the contrary
the patched QEMU is a bit faster:

        old      new
mean    14.83325 14.82660
stddev  0.016930 0.010328
min     14.819   14.818
max     14.854   14.883
median  14.8225  14.8255
count   20       20

Paolo