[libvirt] [PATCH v6 0/2] Add support for qcow2 cache

[John Ferlan]

On 09/18/2017 11:45 PM, Liu Qing wrote:
> Qcow2 small IO random write performance will drop dramatically if the l2
> cache table could not cover the whole disk. This will be a lot of l2
> cache table RW operations if cache miss happens frequently.
>  
> This patch exports the qcow2 driver parameter
> l2-cache-size/refcount-cache-size, first added in Qemu 2.2, and
> cache-clean-interval, first added in Qemu 2.5, in libvirt.
> 
> change since v4: removed unnecessary cache error check
> 
> Liu Qing (2):
>   conf, docs: Add qcow2 cache configuration support

According to what you added for the v5 - there's an upstream bz that
could be associated with this work.  Is this something that should be
added to the commit message so that we can "track" where the idea comes
from?

Beyond that - I agree setting policy is not the business we want to be
in. I just figured I'd throw it out there. I didn't read all of the qemu
links from the bz about thoughts on this - too many links too much to
follow not enough time/desire to think about it.

I'm not against pushing these patches, but would like to at least make
sure Peter isn't 100% against them. I agree the attributes are really
painful to understand, but it's not the first time we've added some
attribute that comes with a beware of using this unless you know what
you're doing.

John

>   qemu: add capability checking for qcow2 cache configuration
> 
>  docs/formatdomain.html.in                          | 41 +++++++++
>  docs/schemas/domaincommon.rng                      | 35 ++++++++
>  src/conf/domain_conf.c                             | 97 ++++++++++++++++++++--
>  src/qemu/qemu_capabilities.c                       | 11 +++
>  src/qemu/qemu_capabilities.h                       |  5 ++
>  src/qemu/qemu_command.c                            | 33 ++++++++
>  src/qemu/qemu_driver.c                             |  5 ++
>  src/util/virstoragefile.c                          |  3 +
>  src/util/virstoragefile.h                          |  6 ++
>  tests/qemucapabilitiesdata/caps_2.5.0.x86_64.xml   |  3 +
>  .../caps_2.6.0-gicv2.aarch64.xml                   |  3 +
>  .../caps_2.6.0-gicv3.aarch64.xml                   |  3 +
>  tests/qemucapabilitiesdata/caps_2.6.0.ppc64le.xml  |  3 +
>  tests/qemucapabilitiesdata/caps_2.6.0.x86_64.xml   |  3 +
>  tests/qemucapabilitiesdata/caps_2.7.0.s390x.xml    |  3 +
>  tests/qemucapabilitiesdata/caps_2.7.0.x86_64.xml   |  3 +
>  tests/qemucapabilitiesdata/caps_2.8.0.s390x.xml    |  3 +
>  tests/qemucapabilitiesdata/caps_2.8.0.x86_64.xml   |  3 +
>  tests/qemucapabilitiesdata/caps_2.9.0.ppc64le.xml  |  3 +
>  tests/qemucapabilitiesdata/caps_2.9.0.s390x.xml    |  3 +
>  tests/qemucapabilitiesdata/caps_2.9.0.x86_64.xml   |  3 +
>  .../qemuxml2argv-disk-drive-qcow2-cache.args       | 28 +++++++
>  .../qemuxml2argv-disk-drive-qcow2-cache.xml        | 43 ++++++++++
>  tests/qemuxml2argvtest.c                           |  4 +
>  .../qemuxml2xmlout-disk-drive-qcow2-cache.xml      | 43 ++++++++++
>  tests/qemuxml2xmltest.c                            |  1 +
>  26 files changed, 384 insertions(+), 7 deletions(-)
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.args
>  create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.xml
>  create mode 100644 tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-qcow2-cache.xml
>