[Qemu-devel] [Bug 601946] Re: [Feature request] qemu-img multi-threaded compressed image conversion

[Mike Ashton]

The compression in this case is certainly chunked already, otherwise you
couldn't implement a pseudo block device without reading the entire
stream to read the last block!  As the data in the new disk is
necessarily chunk compressed, parallelisation is perfect feasible, it's
just a question of the algorithm you use to arbitrate the work between
the threads, which may need some thought as you'd likely be navigating a
tree structure.

There's no question that Jes' suggestion would create a 12x speed up for
me, and there's pretty standard off the shelf server hardware with 48
cores.  As Jan-Simon Möller points out, being single-threaded and
single-process isn't much of an option any more.  If one is trying to
compress, say, a 4TB virtual disk image then using a little over 2% of
the available CPU time meaning you have to wait a week is going to be...
frustrating :)

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https://bugs.launchpad.net/bugs/601946

Title:
  [Feature request] qemu-img multi-threaded compressed image conversion

Status in QEMU:
  New

Bug description:
  Feature request:
  qemu-img multi-threaded compressed image conversion

  Suppose I want to convert raw image to compressed qcow2. Multi-
  threaded conversion will be much faster, because bottleneck is
  compressing data.

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