[libvirt] [PATCH] examples: Introduce domtop

[Ján Tomko]

On 07/16/2014 03:53 PM, Michal Privoznik wrote:
> There's this question on the list that is asked over and over again.
> How do I get {cpu, memory, ...} usage in percentage? Or its modified
> version: How do I plot nice graphs like virt-manager does?
> 
> It would be nice if we have an example to inspire people. And that's
> what domtop should do. Yes, it could be written in different ways, but
> I've chosen this one as I think it show explicitly what users need to
> implement in order to imitate virt-manager's graphing.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  .gitignore                  |   1 +
>  Makefile.am                 |   2 +-
>  cfg.mk                      |   2 +-
>  configure.ac                |   1 +
>  examples/domtop/Makefile.am |  27 +++
>  examples/domtop/domtop.c    | 388 ++++++++++++++++++++++++++++++++++++++++++++
>  libvirt.spec.in             |   2 +-
>  7 files changed, 420 insertions(+), 3 deletions(-)
>  create mode 100644 examples/domtop/Makefile.am
>  create mode 100644 examples/domtop/domtop.c

> +
> +static void
> +print_cpu_usage(const char *dom_name,
> +                size_t cpu,
> +                size_t ncpus,
> +                unsigned long long then,
> +                virTypedParameterPtr then_params,
> +                size_t then_nparams,
> +                unsigned long long now,
> +                virTypedParameterPtr now_params,
> +                size_t now_nparams)
> +{
> +    size_t i, j, k;
> +    size_t nparams = now_nparams;
> +
> +    if (then_nparams != now_nparams) {
> +        /* this should not happen (TM) */
> +        ERROR("parameters counts don't match");
> +        return;
> +    }
> +
> +    for (i = 0; i < ncpus; i++) {
> +        size_t pos;
> +        double usage;
> +
> +        /* check if the vCPU is in the maps */
> +        if (now_params[i * nparams].type == 0 ||
> +            then_params[i * then_nparams].type == 0)
> +            continue;
> +
> +        for (j = 0; j < nparams; j++) {
> +            pos = i * nparams + j;
> +            if (STREQ(then_params[pos].field, VIR_DOMAIN_CPU_STATS_CPUTIME) ||
> +                STREQ(then_params[pos].field, VIR_DOMAIN_CPU_STATS_VCPUTIME))
> +                break;
> +        }
> +
> +        if (j == nparams) {
> +            ERROR("unable to find %s", VIR_DOMAIN_CPU_STATS_CPUTIME);
> +            return;
> +        }
> +
> +        DEBUG("now_params=%llu then_params=%llu now=%llu then=%llu",
> +              now_params[pos].value.ul, then_params[pos].value.ul, now, then);
> +
> +        /* @now_params and @then_params are in nanoseconds, @now and @then are
> +         * in microseconds. In ideal world, we would translate them both into
> +         * the same scale, divide one by another and multiply by factor of 100
> +         * to get percentage. However, the count of floating point operations
> +         * performed has a bad affect on the precision, so instead of dividing

s/affect/effect/

> +         * @now_params and @then_params by 1000 and then multiplying again by
> +         * 100, we divide only once by 10 and get the same result. */
> +        usage = (now_params[pos].value.ul - then_params[pos].value.ul) /
> +                (now - then) / 10;
> +
> +        printf("CPU%zu: %.2lf\n", cpu + i, usage);

I think printing all the CPUs on one line would look nicer, and it would be
easier to see which numbers are changing.

ACK

Jan

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