[Virtio-fs] [RFC PATCH 0/2] add stat tools for virtiofsd

[Gang Deng <gavin.dg@linux.alibaba.com>]

There exist two components: vtrace && vstat. vtrace is embeded in virtiofsd,
it will put raw statistics data into share memory. Then the vstat tool could
parse it and do some post processing works. The performance overhead of
vtrace is very small because it does very simple things.

For example, if we call open(2)/close(2) frequently in guest, and
randwite a file whose length is greater than the size of dax window.
We'll get the output as below:

op                        inflt         op/s     svctm/us   %util
FUSE_OPEN(14)                 0      8379.87         3.24   2.71%
FUSE_RELEASE(18)              0      8379.87         1.77   1.48%
FUSE_FLUSH(25)                0      8379.87         2.04   1.71%
FUSE_SETUPMAPPING(48)         1      6393.90        34.72  22.20%
FUSE_REMOVEMAPPING(49)        0      6404.90        37.61  24.09%
TOTAL                         1     37938.39        13.76  52.20%

The meaning of fields:

- op
  The type of fuse requests, 'TOTAL' is sum of all.

- inflt
  The number of the inflight requests, it must be ethier 0 or 1 because
  virtiofsd can only process fuse requests serially.

- op/s
  The number of fuse requests completed per second.

- svctm/us
  The average service time (in microseconds) for fuse requests.

- %util
  Percentage of elapsed time during which virtiofsd was processing the fuse
  requests.

when virtiofsd is hang, e.g. we support flock in host (just for example,
this has been fxied), we'll get this:

op                        inflt         op/s     svctm/us   %util
FUSE_SETLKW(33)               1         0.00         0.00 100.00%
TOTAL                         1         0.00         0.00 100.00%

the utilization is 100% and op/s equals zero, it indicates hang.

If virtiofsd is idle, then the output looks like this:

op                        inflt         op/s     svctm/us   %util
TOTAL                         0         0.00         0.00   0.00%

TODO:
 Vstat was designed to scan VIRTIOFS_TRACE_DIR directory to get all virtiofs
 devices. However it's not supported yet. Because virtiofsd couldn't unlink
 the trace file when exited due to the sandboxing, actually we unlink the
 trace file when inited. Then vstat can only access the trace file through
 the /proc/<virtiofs-pid>/fd/<trace-file> (which needs root privilege)
 This should be refactored later if virtiofsd could access /dev/shm
 directory, then vstat can run as nobody and be able to scan all devices
 like iostat tool.

Gang Deng (2):
  virtiofsd: add stat tools
  virtiofsd: support vstat&&vtrace

 Makefile                           |   3 +
 Makefile.objs                      |   1 +
 contrib/virtiofsd/Makefile.objs    |   5 +-
 contrib/virtiofsd/fuse_i.h         |   1 +
 contrib/virtiofsd/fuse_lowlevel.c  |  11 +
 contrib/virtiofsd/fuse_lowlevel.h  |   1 +
 contrib/virtiofsd/helper.c         |   4 +-
 contrib/virtiofsd/passthrough_ll.c |   7 +
 contrib/virtiofsd/vstat.c          | 680 +++++++++++++++++++++++++++++
 contrib/virtiofsd/vtrace.c         |  95 ++++
 contrib/virtiofsd/vtrace.h         |  53 +++
 11 files changed, 859 insertions(+), 2 deletions(-)
 create mode 100644 contrib/virtiofsd/vstat.c
 create mode 100644 contrib/virtiofsd/vtrace.c
 create mode 100644 contrib/virtiofsd/vtrace.h

-- 
2.20.1.7.g153144c