[Qemu-devel] Defaulting SD_OPTS to cache=writeback

[David Gilbert]

Hi,
  Write performance on the SD emulation on ARM is rather painful with
the default empty SD_OPTS; it's
getting something like 130KB/s on the vexpress model  With
cache=writeback this goes up to a sensible
8MB/s. (This is with the file on an LUKS encrypted lvm partition that
is my home directory on an Ubuntu Lucid
install on my core 2 laptop).

The impact is probably so bad because most of the writes are done
using the SD card's native 512byte block size
which turns into a read/modify/write.

Is it reasonable to set SD_OPTS to "cache=writeback" ?  If people want
other options they can always use -drive,
but having the default give 130KB/s is nasty.

Dave