Re: [Xen-devel] [PATCH v1 3/3] xl: enable per-VCPU extratime flag for RTDS

[Meng Xu <xumengpanda@xxxxxxxxx>]

On Sun, Aug 6, 2017 at 12:22 PM, Meng Xu <mengxu@xxxxxxxxxxxxx> wrote:
> Change main_sched_rtds and related output functions to support
> per-VCPU extratime flag.
>
> Signed-off-by: Meng Xu <mengxu@xxxxxxxxxxxxx>
>
> ---
> Changes from RFC v1
> Changes work_conserving flag to extratime flag
> ---
>  tools/xl/xl_cmdtable.c |  3 ++-
>  tools/xl/xl_sched.c    | 56 
> ++++++++++++++++++++++++++++++++++----------------
>  2 files changed, 40 insertions(+), 19 deletions(-)
>
> diff --git a/tools/xl/xl_cmdtable.c b/tools/xl/xl_cmdtable.c
> index 2c71a9f..88933a4 100644
> --- a/tools/xl/xl_cmdtable.c
> +++ b/tools/xl/xl_cmdtable.c
> @@ -272,12 +272,13 @@ struct cmd_spec cmd_table[] = {
>      { "sched-rtds",
>        &main_sched_rtds, 0, 1,
>        "Get/set rtds scheduler parameters",
> -      "[-d <Domain> [-v[=VCPUID/all]] [-p[=PERIOD]] [-b[=BUDGET]]]",
> +      "[-d <Domain> [-v[=VCPUID/all]] [-p[=PERIOD]] [-b[=BUDGET]] 
> [-e[=EXTRATIME]]]",
>        "-d DOMAIN, --domain=DOMAIN     Domain to modify\n"
>        "-v VCPUID/all, --vcpuid=VCPUID/all    VCPU to modify or output;\n"
>        "               Using '-v all' to modify/output all vcpus\n"
>        "-p PERIOD, --period=PERIOD     Period (us)\n"
>        "-b BUDGET, --budget=BUDGET     Budget (us)\n"
> +      "-e EXTRATIME, --extratime=EXTRATIME EXTRATIME (1=yes, 0=no)\n"

Hi Dario,

I kept the EXTRATIME value for -e option because: (1) it may be more
intuitive for users; (2) it needs much less code change than the input
style that does not need EXTRATIME value.

As to (1), if users want to set some VCPUs with extratime flag set and
some with extratime flag clear, there are two types of input:
(a) xl sched-rtds -d 1 -v 1 -p 10000 -b 4000 -e 0 -v 2 -p 10000 -b
4000 -e 1 -v 5 -p 10000 -b 4000 -e 0
(b) xl sched-rtds -d 1 -v 1 -p 10000 -b 4000 -v 2 -p 10000 -b 4000 -e
1 -v 5 -p 10000 -b 4000
I felt that the style (a) is more intuitive and the input commands
have very static pattern, i.e., each vcpu must have -v -p -b -e
options set.

As to (2), if we go with -e without EXTRATIME, we will have to keep
track of the vcpu that has no -e option. I thought about this option,
we can pre-set the extratime value to false when -v option is
assigned:
    case 'v':
    ...
    extratimes[v_index]  = 0;

and set the extratimes[v_index] = 0 when -e is set.

This approach is not very neat in the code: we have to reallocate
memory for extratimes array when its size is not enough; we also have
to deal with the special case when -e is set before -v, such as the
command "xl sched-rtds -p 10000 -b 4000 -e -v 0"

Best,

Meng

-----------
Meng Xu
PhD Candidate in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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