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Re: [Qemu-block] [PATCH 0/7] discard blockstats

From: Anton Nefedov
Subject: Re: [Qemu-block] [PATCH 0/7] discard blockstats
Date: Mon, 20 Aug 2018 13:02:35 +0300
User-agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 17/8/2018 8:27 PM, Paolo Bonzini wrote:
On 20/11/2017 17:50, Anton Nefedov wrote:
qmp query-blockstats provides stats info for write/read/flush ops.

Patches 1-5 implement the similar for discard (unmap) command for scsi
and ide disks.
Discard stat "unmap_ops / unmap_bytes" is supposed to account the ops that
have completed without an error.

However, discard operation is advisory. Specifically,
  - common block layer ignores ENOTSUP error code.
    That might be returned if the block driver does not support discard,
    or discard has been configured to be ignored.
  - format drivers such as qcow2 may ignore discard if they were configured
    to ignore that, or if the corresponding area is already marked unused
    (unallocated / zero clusters).

And what is actually useful is the number of bytes actually discarded
down on the host filesystem.
To achieve that, driver-specific statistics has been added to blockstats
(patch 7).
With patch 6, file-posix driver accounts discard operations on its level too.

query-blockstat result:

(note the difference between blockdevice unmap and file discard stats. qcow2
sends a few ops down to the file as the clusters are actually unallocated
on qcow2 level)

{"return": [
{"device": "drive-scsi0-0-0-0"
   "parent": {
     "stats": {
      "unmap_operations": 0
      "unmap_merged": 0
       "flush_total_time_ns": 0
       "wr_highest_offset": 8111718400
       "invalid_wr_operations": 0
       "invalid_rd_operations": 0}
     "node-name": "#block047"
    "driver_stats": {
      "type": "file"
      "data": {
        "discard_bytes_ok": 1572864
        "discard_nb_failed": 0
        "discard_nb_ok": 5}}}
   "stats": {
   "unmap_operations": 472
   "unmap_merged": 0
     "flush_total_time_ns": 44530540
     "wr_highest_offset": 7106662400
     "wr_total_time_ns": 45518856
     "failed_wr_operations": 0
     "failed_rd_operations": 0
     "wr_merged": 0
     "wr_bytes": 889856
     "timed_stats": []
    "failed_unmap_operations": 0
     "failed_flush_operations": 0
     "account_invalid": true
     "rd_total_time_ns": 3306264098
    "invalid_unmap_operations": 0
     "flush_operations": 18
     "wr_operations": 120
    "unmap_bytes": 12312014848
     "rd_merged": 0
     "rd_bytes": 137103360
    "unmap_total_time_ns": 22664692
     "invalid_flush_operations": 0
     "account_failed": true
     "idle_time_ns": 437316567
     "rd_operations": 5636
     "invalid_wr_operations": 0
     "invalid_rd_operations": 0}
   "node-name": "#block128"}

   {"device": "drive-ide0-0-0"

Anton Nefedov (7):
   qapi: add unmap to BlockDeviceStats
   ide: account UNMAP (TRIM) operations
   scsi: store unmap offset and nb_sectors in request struct
   scsi: move unmap error checking to the complete callback
   scsi: account unmap operations
   file-posix: account discard operations
   qapi: query-blockstat: add driver specific file-posix stats

  qapi/block-core.json       | 57 ++++++++++++++++++++++++++++++++++++++++++++++
  include/block/accounting.h |  1 +
  include/block/block.h      |  1 +
  include/block/block_int.h  |  1 +
  block.c                    |  9 ++++++++
  block/file-posix.c         | 42 ++++++++++++++++++++++++++++++++--
  block/qapi.c               | 11 +++++++++
  hw/ide/core.c              | 12 ++++++++++
  hw/scsi/scsi-disk.c        | 29 ++++++++++++++---------
  9 files changed, 150 insertions(+), 13 deletions(-)

Hey, looks like this series has fallen through the cracks.  Anton, are
you going to send an updated version?




yes, and v3 was the latest

I will make a few rebase fixups and resend it soon.


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