File access in mounted volumes extremely slow, CPU bound

Docker Desktop
103

Same for me:

$ docker version
Client:
 Version:      1.12.0-rc2
 API version:  1.24
 Go version:   go1.6.2
 Git commit:   906eacd
 Built:        Fri Jun 17 20:35:33 2016
 OS/Arch:      darwin/amd64
 Experimental: true

Server:
 Version:      1.12.0-rc2
 API version:  1.24
 Go version:   go1.6.2
 Git commit:   a7119de
 Built:        Fri Jun 17 22:09:20 2016
 OS/Arch:      linux/amd64
 Experimental: true

Not a volume at all:

/tmp # time dd if=/dev/zero of=test.dat bs=1024 count=100000
100000+0 records in
100000+0 records out
real	0m 0.37s
user	0m 0.02s
sys	0m 0.35s

Mounted volume via docker-compose:

/var/www/html/var # time dd if=/dev/zero of=test.dat bs=1024 count=100000
100000+0 records in
100000+0 records out
real	0m 33.31s
user	0m 0.15s
sys	0m 2.55s

100x times!! Seriously?