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Re: [libvirt] [PATCH v2] qemu: Add option to enable/disable IOEventFD feature



On Tue, May 17, 2011 at 04:49:17PM +0200, Michal Privoznik wrote:
> This feature allows QEMU to achieve higher throughput, but is available
> only in recent versions. It is accessible via ioeventfd attribute
> with accepting values 'on', 'off'. Only experienced users needs to set
> this, because QEMU defaults to 'on', meaning higher performance.
> Translates into virtio-{blk|net}-pci.ioeventfd option.
> ---
> diff to v1:
> - rebase to current HEAD
> 
>  docs/formatdomain.html.in    |   15 ++++++++++++-
>  docs/schemas/domain.rng      |   14 +++++++++++++
>  src/conf/domain_conf.c       |   44 +++++++++++++++++++++++++++++++++++++++++-
>  src/conf/domain_conf.h       |   12 +++++++++++
>  src/libvirt_private.syms     |    2 +
>  src/qemu/qemu_capabilities.c |    2 +
>  src/qemu/qemu_capabilities.h |    1 +
>  src/qemu/qemu_command.c      |   23 +++++++++++++++++++++
>  tests/qemuhelptest.c         |    3 +-
>  9 files changed, 112 insertions(+), 4 deletions(-)
> 
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 989dcf6..a4d7cbd 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -767,7 +767,7 @@
>      </disk>
>        ...
>      <disk type='network'>
> -      <driver name="qemu" type="raw" io="threads"/>
> +      <driver name="qemu" type="raw" io="threads" ioeventfd="on"/>
>        <source protocol="sheepdog" name="image_name">
>          <host name="hostname" port="7000"/>
>        </source>
> @@ -851,6 +851,11 @@
>              policies on I/O; qemu guests support "threads" and
>              "native". <span class="since">Since 0.8.8</span>
>            </li>
> +          <li>
> +           The optional <code>ioeventfd</code> attribute enables or disables
> +           IOEventFD feature for virtqueue notify. The value can be either
> +           'on' or 'off'.
> +            <span class="since">Since 0.9.2 (QEMU and KVM only)</span>

This is a qemu specific attribute name & description. IMHO we shouldn't
be exposing that directly. Who even knows what effect it actually has
on the guests...

Daniel
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