Re: [Xen-devel] [PATCH 04/16] xen: sched: implement .init_pdata in all schedulers

[Juergen Gross <jgross@xxxxxxxx>]

On 18/03/16 20:04, Dario Faggioli wrote:
> by borrowing some of the code of .alloc_pdata, i.e.,
> the bits that perform initializations, leaving only
> actual allocations in there, when any, which is the
> case for Credit1 and RTDS.
> 
> On the other hand, in Credit2, since we don't really
> need any per-pCPU data allocation, everything that was
> being done in .alloc_pdata, is now done in .init_pdata.
> And the fact that now .alloc_pdata can be left undefined,
> allows us to just get rid of it.
> 
> Still for Credit2, the fact that .init_pdata is called
> during CPU_STARTING (rather than CPU_UP_PREPARE) kills
> the need for the scheduler to setup a similar callback
> itself, simplifying the code.
> 
> And thanks to such simplification, it is now also ok to
> move some of the logic meant at double checking that a
> cpu was (or was not) initialized, into ASSERTS (rather
> than an if() and a BUG_ON).
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Meng Xu <mengxu@xxxxxxxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> ---
>  xen/common/sched_credit.c  |   20 +++++++++---
>  xen/common/sched_credit2.c |   72 
> +++-----------------------------------------
>  xen/common/sched_rt.c      |    9 ++++--
>  3 files changed, 26 insertions(+), 75 deletions(-)
> 
> diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
> index 288749f..d4a0f5e 100644
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -526,8 +526,6 @@ static void *
>  csched_alloc_pdata(const struct scheduler *ops, int cpu)
>  {
>      struct csched_pcpu *spc;
> -    struct csched_private *prv = CSCHED_PRIV(ops);
> -    unsigned long flags;
>  
>      /* Allocate per-PCPU info */
>      spc = xzalloc(struct csched_pcpu);
> @@ -540,6 +538,19 @@ csched_alloc_pdata(const struct scheduler *ops, int cpu)
>          return ERR_PTR(-ENOMEM);
>      }
>  
> +    return spc;
> +}
> +
> +static void
> +csched_init_pdata(const struct scheduler *ops, void *pdata, int cpu)
> +{
> +    struct csched_private *prv = CSCHED_PRIV(ops);
> +    struct csched_pcpu * const spc = pdata;
> +    unsigned long flags;
> +
> +    /* cpu data needs to be allocated, but STILL uninitialized */
> +    ASSERT(spc && spc->runq.next == spc->runq.prev && spc->runq.next == 
> NULL);

This looks weird. I'd prefer:

ASSERT(spc && spc->runq.next == NULL && spc->runq.prev == NULL);

> +
>      spin_lock_irqsave(&prv->lock, flags);
>  
>      /* Initialize/update system-wide config */
> @@ -560,16 +571,12 @@ csched_alloc_pdata(const struct scheduler *ops, int cpu)
>      INIT_LIST_HEAD(&spc->runq);
>      spc->runq_sort_last = prv->runq_sort;
>      spc->idle_bias = nr_cpu_ids - 1;
> -    if ( per_cpu(schedule_data, cpu).sched_priv == NULL )
> -        per_cpu(schedule_data, cpu).sched_priv = spc;
>  
>      /* Start off idling... */
>      BUG_ON(!is_idle_vcpu(curr_on_cpu(cpu)));
>      cpumask_set_cpu(cpu, prv->idlers);
>  
>      spin_unlock_irqrestore(&prv->lock, flags);
> -
> -    return spc;
>  }
>  
>  #ifndef NDEBUG
> @@ -2051,6 +2058,7 @@ static const struct scheduler sched_credit_def = {
>      .alloc_vdata    = csched_alloc_vdata,
>      .free_vdata     = csched_free_vdata,
>      .alloc_pdata    = csched_alloc_pdata,
> +    .init_pdata     = csched_init_pdata,
>      .free_pdata     = csched_free_pdata,
>      .alloc_domdata  = csched_alloc_domdata,
>      .free_domdata   = csched_free_domdata,
> diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
> index 36dc9ee..b1642a8 100644
> --- a/xen/common/sched_credit2.c
> +++ b/xen/common/sched_credit2.c
> @@ -1968,7 +1968,8 @@ static void deactivate_runqueue(struct csched2_private 
> *prv, int rqi)
>      cpumask_clear_cpu(rqi, &prv->active_queues);
>  }
>  
> -static void init_pcpu(const struct scheduler *ops, int cpu)
> +static void
> +csched2_init_pdata(const struct scheduler *ops, void *pdata, int cpu)
>  {
>      unsigned rqi;
>      unsigned long flags;
> @@ -1978,12 +1979,7 @@ static void init_pcpu(const struct scheduler *ops, int 
> cpu)
>  
>      spin_lock_irqsave(&prv->lock, flags);
>  
> -    if ( cpumask_test_cpu(cpu, &prv->initialized) )
> -    {
> -        printk("%s: Strange, cpu %d already initialized!\n", __func__, cpu);
> -        spin_unlock_irqrestore(&prv->lock, flags);
> -        return;
> -    }
> +    ASSERT(!cpumask_test_cpu(cpu, &prv->initialized));
>  
>      /* Figure out which runqueue to put it in */
>      rqi = 0;
> @@ -2033,20 +2029,6 @@ static void init_pcpu(const struct scheduler *ops, int 
> cpu)
>      return;
>  }
>  
> -static void *
> -csched2_alloc_pdata(const struct scheduler *ops, int cpu)
> -{
> -    /* Check to see if the cpu is online yet */
> -    /* Note: cpu 0 doesn't get a STARTING callback */

Sorry if I missed it in an other patch: Where is the init_pdata hook
being called for cpu 0?


Juergen

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