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

[max]

Hi Mohan, 
this parameter provide significant improvement in big file access/write: 
--------------------------------------------------------------------------------------------
VirtFS on /srv/shared type 9p (rw,trans=virtio,version=9p2000.L,msize=262144)

$ dd if=/dev/zero of=test count=100000 bs=16384
100000+0 records in
100000+0 records out
1638400000 bytes (1.6 GB) copied, 36.3589 s, 45.1 MB/s

l$ dd if=/dev/zero of=test count=100000 
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 25.6597 s, 2.0 MB/s

$ dd if=/dev/zero of=test count=1024 bs=262144
1024+0 records in
1024+0 records out
268435456 bytes (268 MB) copied, 3.41936 s, 78.5 MB/s

Speed of copy for large file ~45MB/s (read and write from the same disk). 
---------------------------------------------------------------------------------------------
But Host: 
time ls -lahs bam.unsorted/
many files: 
real    0m0.053s
user    0m0.004s
sys     0m0.036s

VM: 
real    0m4.449s
user    0m0.012s
sys     0m0.136s
--------------------------------------------------------
So we have delays on the first file access. 
Is it possible to resolve this issue?

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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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