Re: [Xen-devel] [PATCH] full support of setting scheduler parameters on domain creation

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 05/21/2012 02:07 PM, Ian Campbell wrote:
> On Mon, 2012-05-21 at 12:46 +0100, Juergen Gross wrote:
> > Obtains current scheduler parameters before modifying any settings specified
> > via domain config. Only specified settings must be modified, of course!
> I presume this will fix the
> libxl: error: libxl.c:3208:libxl_sched_credit_domain_set: Cpu weight out
> of range, valid values are within range from 1 to 65535
> warning we are currently seeing? Thanks!
>
> > @@ -233,6 +233,14 @@ libxl_sched_params = Struct("sched_param
> >       ("slice",        integer),
> >       ("latency",      integer),
> >       ("extratime",    integer),
> > +    ("set_weight",       bool),
> > +    ("set_cap",          bool),
> > +    ("set_tslice_ms",    bool),
> > +    ("set_ratelimit_us", bool),
> > +    ("set_period",       bool),
> > +    ("set_slice",        bool),
> > +    ("set_latency",      bool),
> > +    ("set_extratime",    bool),
> Rather than doing this it would be preferable to identify some specific
> value which means "default" for each of these fields. Generally this
> would be either 0 (preferred if possible) or ~0 or -1. You can then
> describe this in the IDL using the "init_val" property on each field.
> e.g.:
>
> @@ -225,7 +225,7 @@ libxl_domain_create_info = Struct("domai
>   MemKB = UInt(64, init_val = "LIBXL_MEMKB_DEFAULT")
>
>   libxl_sched_params = Struct("sched_params",[
> -    ("weight",       integer),
> +    ("weight",       integer, {'init_val': -1}),
>       ("cap",          integer),
>       ("tslice_ms",    integer),
>       ("ratelimit_us", integer),
>
> (just as an illustration of a non-zero default, I suspect 0 would
> actually be a fine default value for weight, and 0 is the default
> init_val)
>
> Then libxl_sched_params_init, which xl must call (perhaps indirectly,
> e.g. via libxl_domain_build_info_init) would set these defaults and xl
> would override them from the config and libxl would only set those which
> were non-default.
Hmm. Scheduling parameters are handled in the hypervisor. I don't want to
export the knowledge about semantics to the tools. If this is no problem,
why can't I just set the defaults in the tools and omit asking the
hypervisor for the current settings?

Additionally there are parameters (well, one parameter) which apply to
multiple schedulers. Just by chance -1 would be invalid for all of them,
but I don't like to hard code this coincidence.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html


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