This series do standard basic things:
- it creates intermediate buffer for all writes from QEMU migration code
  to QCOW2 image,
- this buffer is sent to disk asynchronously, allowing several writes to
  run in parallel.

In general, migration code is fantastically inefficent (by observation),
buffers are not aligned and sent with arbitrary pieces, a lot of time
less than 100 bytes at a chunk, which results in read-modify-write
operations with non-cached operations. It should also be noted that all
operations are performed into unallocated image blocks, which also suffer
due to partial writes to such new clusters.

This patch series is an implementation of idea discussed in the RFC
posted by Denis
https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg01925.html
Results with this series over NVME are better than original code
                original     rfc    this
cached:          1.79s      2.38s   1.27s
non-cached:      3.29s      1.31s   0.81s

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
CC: Denis Plotnikov <dplotnikov@virtuozzo.com>

Patchew URL: https://patchew.org/QEMU/20200610144129.27659-1-den@openvz.org/



Hi,

This series failed the docker-quick@centos7 build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
make docker-image-centos7 V=1 NETWORK=1
time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
=== TEST SCRIPT END ===

  CC      crypto/hash.o
  CC      crypto/hash-nettle.o
/tmp/qemu-test/src/block/qcow2.c: In function 'qcow2_co_vmstate_task_entry':
/tmp/qemu-test/src/block/qcow2.c:5147:5: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     return err;
     ^
cc1: all warnings being treated as errors
  CC      crypto/hmac.o
  CC      crypto/hmac-nettle.o
make: *** [block/qcow2.o] Error 1
make: *** Waiting for unfinished jobs....
  CC      crypto/desrfb.o
Traceback (most recent call last):
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=3bb6d855342d412ca997d990b1688b3c', '-u', '1001', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=1', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-0hsvevb2/src/docker-src.2020-06-10-14.17.46.12598:/var/tmp/qemu:z,ro', 'qemu:centos7', '/var/tmp/qemu/run', 'test-quick']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=3bb6d855342d412ca997d990b1688b3c
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-0hsvevb2/src'
make: *** [docker-run-test-quick@centos7] Error 2

real    2m9.722s
user    0m9.192s


The full log is available at
http://patchew.org/logs/20200610144129.27659-1-den@openvz.org/testing.docker-quick@centos7/?type=message.
---
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Please send your feedback to patchew-devel@redhat.com

Patchew URL: https://patchew.org/QEMU/20200610144129.27659-1-den@openvz.org/



Hi,

This series failed the docker-mingw@fedora build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#! /bin/bash
export ARCH=x86_64
make docker-image-fedora V=1 NETWORK=1
time make docker-test-mingw@fedora J=14 NETWORK=1
=== TEST SCRIPT END ===

  BUNZIP2 pc-bios/edk2-i386-code.fd.bz2
  BUNZIP2 pc-bios/edk2-arm-vars.fd.bz2
/tmp/qemu-test/src/block/qcow2.c: In function 'qcow2_co_vmstate_task_entry':
/tmp/qemu-test/src/block/qcow2.c:5147:12: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     return err;
            ^~~
cc1: all warnings being treated as errors
make: *** [/tmp/qemu-test/src/rules.mak:69: block/qcow2.o] Error 1
make: *** Waiting for unfinished jobs....
Traceback (most recent call last):
  File "./tests/docker/docker.py", line 665, in <module>
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=a0327ae2ef3c4163bdd307b30bc90a7c', '-u', '1003', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew2/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-fbvrtr6u/src/docker-src.2020-06-10-14.22.01.21453:/var/tmp/qemu:z,ro', 'qemu:fedora', '/var/tmp/qemu/run', 'test-mingw']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=a0327ae2ef3c4163bdd307b30bc90a7c
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-fbvrtr6u/src'
make: *** [docker-run-test-mingw@fedora] Error 2

real    2m20.791s
user    0m8.483s


The full log is available at
http://patchew.org/logs/20200610144129.27659-1-den@openvz.org/testing.docker-mingw@fedora/?type=message.
---
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Please send your feedback to patchew-devel@redhat.com

Patchew URL: https://patchew.org/QEMU/20200610144129.27659-1-den@openvz.org/



Hi,

This series failed the asan build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
export ARCH=x86_64
make docker-image-fedora V=1 NETWORK=1
time make docker-test-debug@fedora TARGET_LIST=x86_64-softmmu J=14 NETWORK=1
=== TEST SCRIPT END ===

  CC      block/gluster.o
  CC      block/ssh.o
  CC      block/dmg-bz2.o
/tmp/qemu-test/src/block/qcow2.c:5139:9: error: variable 'err' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
    if (t->bytes != 0) {
        ^~~~~~~~~~~~~
/tmp/qemu-test/src/block/qcow2.c:5147:12: note: uninitialized use occurs here
---
           ^
            = 0
1 error generated.
make: *** [/tmp/qemu-test/src/rules.mak:69: block/qcow2.o] Error 1
make: *** Waiting for unfinished jobs....
Traceback (most recent call last):
  File "./tests/docker/docker.py", line 665, in <module>
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=213a8da69081459b91db63888e1cc6a0', '-u', '1001', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=x86_64-softmmu', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-v54hgiy2/src/docker-src.2020-06-10-14.20.39.19315:/var/tmp/qemu:z,ro', 'qemu:fedora', '/var/tmp/qemu/run', 'test-debug']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=213a8da69081459b91db63888e1cc6a0
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-v54hgiy2/src'
make: *** [docker-run-test-debug@fedora] Error 2

real    4m8.609s
user    0m8.917s


The full log is available at
http://patchew.org/logs/20200610144129.27659-1-den@openvz.org/testing.asan/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com