Re: [Xen-devel] [PATCH] xen: debug_registers_trap, perf_counters_trap, and "static_partitioning"

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 31/05/2019 16:00, Stefano Stabellini wrote:
> Introduce two global parameters to disable debug registers trapping and
> perf counters trapping. They are only safe to use in static partitiong
> scenarios where sched=null is used -- vcpu cannot be migrated from one
> pcpu to the next.
>
> Introduce a new simple umbrella command line option
> "static_partitioning" that enables vwfi=native, sched=null, and also
> sets debug_registers_trap and perf_counters_trap to false.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Dario Faggioli <dfaggioli@xxxxxxxx>
> ---
> This is not ideal. The best course of action would be to implement
> proper context switching of all the necessary debug and perf counters
> registers. This is an imperfect shortcut, which could reasonably be left
> out of the upstream tree but I shared it with others for their
> convenience.
> ---
>  xen/arch/arm/traps.c    | 26 +++++++++++++++++++++++++-
>  xen/common/schedule.c   |  2 +-
>  xen/include/xen/sched.h |  1 +

I see no hunk in docs/ ...

>  3 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 5c18e918b0..d6eaffde23 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -118,6 +118,28 @@ static int __init parse_vwfi(const char *s)
>  }
>  custom_param("vwfi", parse_vwfi);
>  
> +static bool debug_registers_trap = true;
> +static bool perf_counters_trap = true;
> +
> +static int __init opt_static_partitioning(const char *s)
> +{
> +    if ( strcmp(s, "true") && 
> +         strcmp(s, "True") &&
> +         strcmp(s, "1") )
> +        return 0;

Please please please don't opencode boolean checking.  I think I've
purged all of it (certainly all that I'm aware of), and this example
isn't remotely compatible with existing boolean options.

Furthermore, you can't make something which looks like a single boolean
option with custom_param(), because you can't make the no- prefix work.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel