Re: [Qemu-devel] [PATCH 2/3] qmp: add query-cpus-fast

[Cornelia Huck <cohuck@redhat.com>]

On Mon, 12 Feb 2018 13:14:31 +0100
Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com> wrote:

> From: Luiz Capitulino <lcapitulino@redhat.com>
> 
> The query-cpus command has an extremely serious side effect:
> it always interrupts all running vCPUs so that they can run
> ioctl calls. This can cause a huge performance degradation for
> some workloads. And most of the information retrieved by the
> ioctl calls are not even used by query-cpus.
> 
> This commit introduces a replacement for query-cpus called
> query-cpus-fast, which has the following features:
> 
>  o Never interrupt vCPUs threads. query-cpus-fast only returns
>    vCPU information maintained by QEMU itself, which should be
>    sufficient for most management software needs
> 
>  o Make "halted" field optional: we only return it if the
>    halted state is maintained by QEMU. But this also gives
>    the option of dropping the field in the future (see below)
> 
>  o Drop irrelevant fields such as "current", "pc" and "arch"
> 
>  o Drop field "halted" since it can't be provided fast reliably
>    and is too volatile on most architectures to be really useful
> 
>  o Rename some fields for better clarification & proper naming
>    standard
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
> ---
>  cpus.c               | 38 ++++++++++++++++++++++++++++
>  hmp-commands-info.hx | 14 +++++++++++
>  hmp.c                | 21 ++++++++++++++++
>  hmp.h                |  1 +
>  qapi-schema.json     | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 144 insertions(+)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>