Re: [Xen-devel] [PATCH v4] schedule: move credit scheduler specific member to its privates

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Wed, 2019-06-12 at 12:35 +0300, Andrii Anisov wrote:
> From: Andrii Anisov <andrii_anisov@xxxxxxxx>
> 
> The vcpu structure member last_run_time is used by credit scheduler
> only.
> In order to get better encapsulation, it is moved from a generic
> structure to the credit scheduler private vcpu definition. Also,
> rename
> the member to last_sched_time in order to reflect that it is the time
> when the vcpu went through the scheduling path.
> 
> With this move we have slight changes in functionality:
>  - last_sched_time is not updated for an idle vcpu. But the idle vcpu
> is,
>    in fact, a per-pcpu stub and never migrates so last_sched_time is
>    meaningless for it.
>  - The value of last_sched_time is updated on every schedule, even if
> the
>    vcpu is not being changed. It is still ok, because last_sched_time
> is
>    only used for runnable vcpu migration decision, and we have it
> correct
>    at that moment. Scheduling parameters and statistics are tracked
> by
>    other entities.
> 
> Reducing code and data usage when not running credit scheduler is
> another
> nice side effect.
> 
> While here, also:
>   - turn last_sched_time into s_time_t, which is more appropriate.
>   - properly const-ify related argument of
> __csched_vcpu_is_cache_hot().
> 
> Signed-off-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
>
Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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