Re: [Xen-devel] [PATCH 1 of 6 v2] xen: sched_credit: improve picking up the idlal CPU for a VCPU

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.12.12 at 03:52, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote:
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -59,6 +59,8 @@
>  #define CSCHED_VCPU(_vcpu)  ((struct csched_vcpu *) (_vcpu)->sched_priv)
>  #define CSCHED_DOM(_dom)    ((struct csched_dom *) (_dom)->sched_priv)
>  #define RUNQ(_cpu)          (&(CSCHED_PCPU(_cpu)->runq))
> +/* Is the first element of _cpu's runq its idle vcpu? */
> +#define IS_RUNQ_IDLE(_cpu)  
> (is_idle_vcpu(__runq_elem(RUNQ(_cpu)->next)->vcpu))
>  
>  
>  /*
> @@ -479,9 +481,14 @@ static int
>       * distinct cores first and guarantees we don't do something stupid
>       * like run two VCPUs on co-hyperthreads while there are idle cores
>       * or sockets.
> +     *
> +     * Notice that, when computing the "idleness" of cpu, we may want to
> +     * discount vc. That is, iff vc is the currently running and the only
> +     * runnable vcpu on cpu, we add cpu to the idlers.
>       */
>      cpumask_and(&idlers, &cpu_online_map, CSCHED_PRIV(ops)->idlers);
> -    cpumask_set_cpu(cpu, &idlers);
> +    if ( current_on_cpu(cpu) == vc && IS_RUNQ_IDLE(cpu) )
> +        cpumask_set_cpu(cpu, &idlers);
>      cpumask_and(&cpus, &cpus, &idlers);
>      cpumask_clear_cpu(cpu, &cpus);
>  
> @@ -489,7 +496,7 @@ static int
>      {
>          cpumask_t cpu_idlers;
>          cpumask_t nxt_idlers;
> -        int nxt, weight_cpu, weight_nxt;
> +        int nxt, nr_idlers_cpu, nr_idlers_nxt;
>          int migrate_factor;
>  
>          nxt = cpumask_cycle(cpu, &cpus);
> @@ -513,12 +520,12 @@ static int
>              cpumask_and(&nxt_idlers, &idlers, per_cpu(cpu_core_mask, nxt));
>          }
>  
> -        weight_cpu = cpumask_weight(&cpu_idlers);
> -        weight_nxt = cpumask_weight(&nxt_idlers);
> +        nr_idlers_cpu = cpumask_weight(&cpu_idlers);
> +        nr_idlers_nxt = cpumask_weight(&nxt_idlers);
>          /* smt_power_savings: consolidate work rather than spreading it */
>          if ( sched_smt_power_savings ?
> -             weight_cpu > weight_nxt :
> -             weight_cpu * migrate_factor < weight_nxt )
> +             nr_idlers_cpu > nr_idlers_nxt :
> +             nr_idlers_cpu * migrate_factor < nr_idlers_nxt )
>          {
>              cpumask_and(&nxt_idlers, &cpus, &nxt_idlers);
>              spc = CSCHED_PCPU(nxt);

Despite you mentioning this in the description, these last two hunks
are, afaict, only renaming variables (and that's even debatable, as
the current names aren't really misleading imo), and hence I don't
think belong in a patch that clearly has the potential for causing
(performance) regressions.

That said - I don't think it will (and even more, I'm agreeable to the
change done).

> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -396,6 +396,9 @@ extern struct vcpu *idle_vcpu[NR_CPUS];
>  #define is_idle_domain(d) ((d)->domain_id == DOMID_IDLE)
>  #define is_idle_vcpu(v)   (is_idle_domain((v)->domain))
>  
> +#define current_on_cpu(_c) \
> +  ( (per_cpu(schedule_data, _c).curr) )
> +

This, imo, really belings into sched-if.h.

Plus - what's the point of double parentheses, when in fact none
at all would be needed?

And finally, why "_c" and not just "c"?

Jan

>  #define DOMAIN_DESTROYED (1<<31) /* assumes atomic_t is >= 32 bits */
>  #define put_domain(_d) \
>    if ( atomic_dec_and_test(&(_d)->refcnt) ) domain_destroy(_d)




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel