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Re: [Qemu-devel] [PATCH v4 0/8] discard blockstats


From: Anton Nefedov
Subject: Re: [Qemu-devel] [PATCH v4 0/8] discard blockstats
Date: Tue, 18 Sep 2018 11:12:44 +0300
User-agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

ping

do you think we might proceed with this? or is there any general doubt
about the idea?

thanks,

On 21/8/2018 12:46 PM, Anton Nefedov wrote:
new in v4:
     - patch 7: discard and write-zeroes code paths had been separated in
       34fa110e: file-posix: Fix write_zeroes with unmap on block devices.
       This patch now only accounts discards that come explicitly
       through .bdrv_co_pdiscard handler.
     - qapi 'Since' clauses changed 3.0 -> 3.1

v3: http://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg03688.html

----

qmp query-blockstats provides stats info for write/read/flush ops.

Patches 1-6 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 8).
With patch 7, 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 fewer ops down to the file as the clusters are actually unallocated
on qcow2 level)

{
   "return": [
     {
       "device": "drive-scsi0-0-0-0",
       "parent": {
       "discard-bytes-ok": 262144,
       "discard-nb-ok": 4,
         "stats": {
         "unmap_operations": 0,
         "unmap_merged": 0,
           "flush_total_time_ns": 0,
           "wr_highest_offset": 8111718400,
           "wr_total_time_ns": 0,
           "failed_wr_operations": 0,
           "failed_rd_operations": 0,
           "wr_merged": 0,
           "wr_bytes": 0,
           "timed_stats": [
],
         "failed_unmap_operations": 0,
           "failed_flush_operations": 0,
           "account_invalid": false,
           "rd_total_time_ns": 0,
         "invalid_unmap_operations": 0,
           "flush_operations": 0,
           "wr_operations": 0,
         "unmap_bytes": 0,
           "rd_merged": 0,
           "rd_bytes": 0,
         "unmap_total_time_ns": 0,
           "invalid_flush_operations": 0,
           "account_failed": false,
           "rd_operations": 0,
           "invalid_wr_operations": 0,
           "invalid_rd_operations": 0
         },
         "node-name": "#block012",
       "driver": "file",
       "discard-nb-failed": 0
       },
       "stats": {
       "unmap_operations": 860,
       "unmap_merged": 0,
         "flush_total_time_ns": 21506733,
         "wr_highest_offset": 13411741696,
         "wr_total_time_ns": 2212749334,
         "failed_wr_operations": 0,
         "failed_rd_operations": 0,
         "wr_merged": 0,
         "wr_bytes": 3426304,
         "timed_stats": [
],
       "failed_unmap_operations": 0,
         "failed_flush_operations": 0,
         "account_invalid": true,
         "rd_total_time_ns": 3617478206,
       "invalid_unmap_operations": 0,
         "flush_operations": 24,
         "wr_operations": 309,
       "unmap_bytes": 11949633536,
         "rd_merged": 0,
         "rd_bytes": 141967360,
       "unmap_total_time_ns": 14871816,
         [..]

Anton Nefedov (8):
   qapi: group BlockDeviceStats fields
   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       | 82 +++++++++++++++++++++++++++++++++++++++-------
  include/block/accounting.h |  1 +
  include/block/block.h      |  1 +
  include/block/block_int.h  |  1 +
  block.c                    |  9 +++++
  block/file-posix.c         | 45 +++++++++++++++++++++++--
  block/qapi.c               | 11 +++++++
  hw/ide/core.c              | 12 +++++++
  hw/scsi/scsi-disk.c        | 29 +++++++++-------
  tests/qemu-iotests/227.out | 18 ++++++++++
  10 files changed, 184 insertions(+), 25 deletions(-)




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