Comment 10 for bug 1847948

Christian,

Using QEMU from comment 6, it improved the performance for numjobs=4 and numjobs=64 cases, respectively:

   READ: bw=1140MiB/s (1195MB/s), 271MiB/s-302MiB/s (284MB/s-317MB/s), io=66.8GiB (71.7GB), run=60001-60001msec
   READ: bw=4271MiB/s (4479MB/s), 30.1MiB/s-82.6MiB/s (31.6MB/s-86.6MB/s), io=250GiB (269GB), run=60001-60003msec

$ dpkg -l | grep ppa1
ii qemu 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el fast processor emulator
ii qemu-block-extra:ppc64el 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el extra block backend modules for qemu-system and qemu-utils
ii qemu-kvm 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU Full virtualization on x86 hardware
ii qemu-system 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries
ii qemu-system-arm 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (arm)
ii qemu-system-common 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (common files)
ii qemu-system-mips 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (mips)
ii qemu-system-misc 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (miscellaneous)
ii qemu-system-ppc 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (ppc)
ii qemu-system-s390x 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (s390x)
ii qemu-system-sparc 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (sparc)
ii qemu-system-x86 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU full system emulation binaries (x86)
ii qemu-user 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU user mode emulation binaries
ii qemu-user-binfmt 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU user mode binfmt registration for qemu-user
ii qemu-utils 1:2.11+dfsg-1ubuntu7.20~ppa1 ppc64el QEMU utilities

Note 0: We booted a newer kernel on the host that contained the patch
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a32295c612c57990d17fb0f41e7134394b2f35f6

Using Bionic kernel 4.15.0-65.74, the performance hasn't changed.
Most likely because Bionic kernel doesn't contain the above patch yet.

Note 1: Kudos to Murilo Vicentini for running the tests and capturing
the numbers.