[Qemu-devel] [Bug 965867] Re: 9p virtual file system on qemu slow

[max]

One of possible problems could be a block size. In this case I am using
ZFS with raidZ 4+1 drives. Each drive has 4Kb block. So optimal block
size is 16384 bytes. By optimizing block size it possible to improve
performance 10 folds but 9p stably provides 10 folds worse performance
than native writes.

Some extra tests: 
---------------------
VM - mapped

$ dd if=/dev/zero of=test count=100000
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 20.7879 s, 2.5 MB/s

$ dd if=/dev/zero of=test count=100000  bs=16384
100000+0 records in
100000+0 records out
1638400000 bytes (1.6 GB) copied, 74.4378 s, 22.0 MB/s
------------------------------------------------------------
Host: 
$ dd if=/dev/zero of=test count=100000
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 1.60118 s, 32.0 MB/s

$ dd if=/dev/zero of=test count=100000  bs=16384
100000+0 records in
100000+0 records out
1638400000 bytes (1.6 GB) copied, 4.89932 s, 334 MB/s


Iggy: I has issue with permission in passthrough mode. Can you give an idea how 
to setup permissions in this mode?

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https://bugs.launchpad.net/bugs/965867

Title:
  9p virtual file system on qemu slow

Status in QEMU:
  New
Status in “qemu-kvm” package in Ubuntu:
  Confirmed

Bug description:
  Hi, 
  The 9p virtual file system is slow. Several examples below: 
  ---------------------------------------------------------
  Host for the first time: 
  $ time ls bam.unsorted/
  ...........................
  real    0m0.084s
  user    0m0.000s
  sys     0m0.028s
  --------------------------------------------------
  Host second and following: 

  real    0m0.009s
  user    0m0.000s
  sys     0m0.008s
  ------------------------------------------------------
  VM for the first time: 
  $ time ls bam.unsorted/
  ................................
  real    0m23.141s
  user    0m0.064s
  sys     0m2.156s
  ------------------------------------------------------
  VM for the second time
  real    0m3.643s
  user    0m0.024s
  sys     0m0.424s
  ----------------------------------------------------

  Copy on host: 
  $ time cp 5173T.root.bak test.tmp
  real    0m30.346s
  user    0m0.004s
  sys     0m5.324s

  $ ls -lahs test.tmp
  2.7G -rw------- 1 oneadmin cloud 2.7G Mar 26 21:47 test.tmp

  ---------------------------------------------------
  $ copy on VM for the same file

  time cp 5173T.root.bak test.tmp

  real    5m46.978s
  user    0m0.352s
  sys     1m38.962s

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