Extended I/O accounting

Here's v4 of the series that implements extended I/O accounting for block devices.

Since part of Max's BlockBackend series has already been merged, this series can now be applied cleanly on top of the master branch without additional dependencies.

Here's the summary of what this series provides:

- New block_acct_failed() and block_acct_invalid() calls. We keep track now of the number of successful, failed and invalid operations (each one separated into read, write and flush). So from the API point of view, BlockDeviceStats contains 6 new fields for those.

- idle_time_ns: time since the last I/O operation.

- New BlockDeviceTimedStats struct: it has statistics for the I/O during a given interval of time. It keeps minimum, maximum and average latencies for read, write and flush operations.

It also keeps the average read and write queue depths.

- New 'stats-intervals' option that allows the user to define the intervals used to keep the aforementioned statistics. An arbitrary number of intervals can be specified, the length of each one is in seconds.

For the API I opted for a colon-separated list of numbers,

      stats-intervals=60:3600:86400

I also considered something a different syntax,

      stats-intervals.0.length=60,
      stats-intervals.1.length=3600,
      stats-intervals.2.length=86400

This one could be useful if we want to specify any other attribute for each interval, but I couldn't come up with any, so I chose the simpler solution.

- Two new options, stats-account-invalid and stats-account-failed, which allow the user to decide whether to count invalid and failed operations when computing the idle time and total latency.

Regards,

Berto

v4:
- Rebase on top of the current master. This series no longer depends on any other.
- patch 8: clarify that interval_length is in seconds [Stefan]
- patch 9: rewrite timed_average_sum() so it does not call qemu_clock_get_ns() twice [Stefan]

v3: https://lists.gnu.org/archive/html/qemu-block/2015-10/msg00785.html
- Rebased on top of the current master and on Max's BlockBackend series v7
- patch 4: minor documentation fixes [Stefan]
- patch 5: s/miliseconds/nanoseconds/ [Stefan]
- patch 6: dropped, there's no "supports_stats" anymore [Stefan]
- patch 7 (now 6): explain why block_acct_invalid() does not update

          total_time_ns[] [Stefan]

- patch 12 (now 11): don't initialize BlockAcctCookie to { 0 }, it's not needed.

v2: https://lists.gnu.org/archive/html/qemu-block/2015-10/msg00161.html
- First complete implementation of the new statistics

v1: https://lists.gnu.org/archive/html/qemu-devel/2015-06/msg03321.html
- Initial series containing only the timed average infrastructure.

Alberto Garcia (21):
xen_disk: Account for flush operations
ide: Account for write operations correctly
block: define 'clock_type' for the accounting code
util: Infrastructure for computing recent averages
block: Add idle_time_ns to BlockDeviceStats
block: Add statistics for failed and invalid I/O operations
block: Allow configuring whether to account failed and invalid ops
block: Compute minimum, maximum and average I/O latencies
block: Add average I/O queue depth to BlockDeviceTimedStats
block: New option to define the intervals for collecting I/O
statistics
qemu-io: Account for failed, invalid and flush operations
block: Use QEMU_CLOCK_VIRTUAL for the accounting code in qtest mode
iotests: Add test for the block device statistics
nvme: Account for failed and invalid operations
virtio-blk: Account for failed and invalid operations
xen_disk: Account for failed and invalid operations
atapi: Account for failed and invalid operations
ide: Account for failed and invalid operations
macio: Account for failed operations
scsi-disk: Account for failed operations
block: Update copyright of the accounting code

 block/accounting.c           | 123 ++++++++++++++-
 block/block-backend.c        |   1 +
 block/qapi.c                 |  51 +++++++
 blockdev.c                   |  53 +++++++
 hmp.c                        |   4 +-
 hw/block/nvme.c              |  11 +-
 hw/block/virtio-blk.c        |   4 +-
 hw/block/xen_disk.c          |  27 +++-
 hw/ide/atapi.c               |  31 ++--
 hw/ide/core.c                |  12 +-
 hw/ide/macio.c               |  12 +-
 hw/scsi/scsi-disk.c          |  46 ++++--
 include/block/accounting.h   |  28 ++++
 include/qemu/timed-average.h |  64 ++++++++
 qapi/block-core.json         | 103 ++++++++++++-
 qemu-io-cmds.c               |   9 ++
 qmp-commands.hx              |  80 +++++++++-
 tests/Makefile               |   4 +
 tests/qemu-iotests/136       | 349 +++++++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/136.out   |   5 +
 tests/qemu-iotests/group     |   1 +
 tests/test-timed-average.c   |  90 +++++++++++
 util/Makefile.objs           |   1 +
 util/timed-average.c         | 231 ++++++++++++++++++++++++++++
 24 files changed, 1292 insertions(+), 48 deletions(-)
 create mode 100644 include/qemu/timed-average.h
 create mode 100644 tests/qemu-iotests/136
 create mode 100644 tests/qemu-iotests/136.out
 create mode 100644 tests/test-timed-average.c
 create mode 100644 util/timed-average.c

2.6.1