Re: [Qemu-devel] [PATCH] 9pfs: add support for IO limits to 9p-local driver

[Eric Blake]

On 09/07/2016 07:39 AM, Pradeep wrote:
> Uses throttling APIs to limit I/O bandwidth and number of operations on the 
> devices which use 9p-local driver.
> 
> Signed-off-by: Pradeep <address@hidden>
>  fsdev/file-op-9p.h      |   3 +
>  fsdev/qemu-fsdev-opts.c |  52 +++++++++++++
>  hw/9pfs/9p-local.c      |  18 ++++-
>  hw/9pfs/9p-throttle.c   | 199 
> ++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/9pfs/9p-throttle.h   |  55 +++++++++++++
>  hw/9pfs/9p.c            |   7 ++
>  hw/9pfs/Makefile.objs   |   1 +
>  7 files changed, 333 insertions(+), 2 deletions(-)
>  create mode 100644 hw/9pfs/9p-throttle.c
>  create mode 100644 hw/9pfs/9p-throttle.h
> 
> Hi All,
> 
> This adds the support for the 9p-local driver.
> For now this functionality can be enabled only through qemu cli options.
> QMP interface and support to other drivers need further extensions.
> To make it simple for other drivers, the throttle code has been put in
> separate files.

CLI-only extensions mean that we can't use it during hotplug.  Are you
sure that blockdev-add won't automatically enable these options, given
that it tries to convert the dictionary passed through QMP back into the
QemuOpts form that matches command line parsing?  Also, aren't these
limits very similar to what is already available in the throttle driver?
Why are we repeating them at the 9p driver, instead of putting a
throttle group BDS in the mix?

> +++ b/fsdev/qemu-fsdev-opts.c
> @@ -37,6 +37,58 @@ static QemuOptsList qemu_fsdev_opts = {
>          }, {
>              .name = "sock_fd",
>              .type = QEMU_OPT_NUMBER,
> +        }, {
> +            .name = "bps",
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "total bytes burst",
> +        }, {
> +            .name = "bps_rd",
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "total bytes read burst",
> +        }, {


At the very least, if we must have multiple throttle implementations,
can they at least share code so that we don't forget to update one when
adding another option to the other?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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