1. 22 Oct, 2009 1 commit
    • Christoph Hellwig's avatar
      virtio_blk: revert QUEUE_FLAG_VIRT addition · f8b12e51
      Christoph Hellwig authored
      It seems like the addition of QUEUE_FLAG_VIRT caueses major performance
      regressions for Fedora users:
      
      	https://bugzilla.redhat.com/show_bug.cgi?id=509383
      	https://bugzilla.redhat.com/show_bug.cgi?id=505695
      
      while I can't reproduce those extreme regressions myself I think the flag
      is wrong.
      
      Rationale:
      
        QUEUE_FLAG_VIRT expands to QUEUE_FLAG_NONROT which casus the queue
        unplugged immediately.  This is not a good behaviour for at least
        qemu and kvm where we do have significant overhead for every
        I/O operations.  Even with all the latested speeups (native AIO,
        MSI support, zero copy) we can only get native speed for up to 128kb
        I/O requests we already are down to 66% of native performance for 4kb
        requests even on my laptop running the Intel X25-M SSD for which the
        QUEUE_FLAG_NONROT was designed.
        If we ever get virtio-blk overhead low enough that this flag makes
        sense it should only be set based on a feature flag set by the host.
      Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      f8b12e51
  2. 16 Oct, 2009 12 commits
  3. 15 Oct, 2009 23 commits
  4. 14 Oct, 2009 4 commits