Re: [PATCH v3 4/6] xen/cpupool: Create different cpupools at boot time

[Luca Fancellu <Luca.Fancellu@arm.com>]

>> +- cpupool-sched (optional)
>> +
>> +    Must be a string having the name of a Xen scheduler, it has no effect when
>> +    used in conjunction of a cpupool-id equal to zero, in that case the
>> +    default Xen scheduler is selected (sched=<...> boot argument).
>> +    Check the sched=<...> boot argument for allowed values.
> 
> I am happy with this version of the device tree bindings, thanks for
> your efforts to update them. Only one comment left: please update the
> description not to include "cpupool-id" given that there is no
> cpupool-id property anymore :-)
> 

Hi Stefano,

Thank you for your review,

Yes I missed that! I will fix in the next serie.

>> 
>> +/*
>> + * pool_cpu_map:   Index is logical cpu number, content is cpupool id, (-1) for
>> + *                 unassigned.
>> + * pool_sched_map: Index is cpupool id, content is scheduler id, (-1) for
>> + *                 unassigned.
>> + */
>> +static int __initdata pool_cpu_map[NR_CPUS]   = { [0 ... NR_CPUS-1] = -1 };
>> +static int __initdata pool_sched_map[NR_CPUS] = { [0 ... NR_CPUS-1] = -1 };
>> +static unsigned int __initdata next_pool_id;
>> +
>> +#ifdef CONFIG_HAS_DEVICE_TREE
> 
> BOOT_TIME_CPUPOOLS depends on HAS_DEVICE_TREE, so it is not possible to
> have BOOT_TIME_CPUPOOLS but not HAS_DEVICE_TREE ?

Yes you are right, the ifdef is not needed at this stage since only arch with device tree are
using it, if x86 would like to implement a command line version then the code will be ifdef-ined
later.

> 
> 
>> +#define BTCPUPOOLS_DT_NODE_NO_REG     (-1)
>> +#define BTCPUPOOLS_DT_NODE_NO_LOG_CPU (-2)
>> +
>> +static int __init get_logical_cpu_from_hw_id(unsigned int hwid)
>> +{
>> +    unsigned int i;
>> +
>> +    for ( i = 0; i < nr_cpu_ids; i++ )
>> +        if ( cpu_physical_id(i) == hwid )
>> +            return i;
>> +
>> +    return -1;
>> +}
> 
> I wonder if there is a better way to implement this function but I am
> not sure. Also, it might be better to avoid premature optimizations.
> 
> That said, we could check first the simple case where hwid==i. Looking
> at various existing device tree, it seems to be the most common case.
> 
> This is not a requirement, just a hand-wavy suggestion. I think the
> patch is also OK as is.
> 

Not sure to understand here, at least on FVP (the first DT I have around), hwid != i,
Or maybe I didn’t understand what you mean

> 
>> +void __init btcpupools_allocate_pools(void)
>> +{
>> +    unsigned int i;
>> +    bool add_extra_cpupool = false;
>> +
>> +    /*
>> +     * If there are no cpupools, the value of next_pool_id is zero, so the code
>> +     * below will assign every cpu to cpupool0 as the default behavior.
>> +     * When there are cpupools, the code below is assigning all the not
>> +     * assigned cpu to a new pool (next_pool_id value is the last id + 1).
>> +     * In the same loop we check if there is any assigned cpu that is not
>> +     * online.
>> +     */
>> +    for ( i = 0; i < nr_cpu_ids; i++ )
>> +        if ( cpumask_test_cpu(i, &cpu_online_map) )
> 
> Let me take this opportunity to explain the unfortunately unwritten
> coding style the way I understand it. I know this is tribal knowledge at
> the moment and I apologize for that.
> 
> If it is a single line statement, we skip the { }, we keep them in all
> other cases.
> 
> So:
> 
>  /* correct */
>  if ( xxx ) {
>      something;
>      something else;
>  }
> 
>  /* correct */
>  if ( xxx ) {
>      for ( yyy ) {
>      }
>  }
> 
>  /* correct */
>  if ( xxx )
>      something single line or 2 lines like a printk that go beyond 80
>      chars, never in case of nested ifs
> 
>  /* not correct */
>  if ( xxx )
>      something
>      multi
>      line;
> 
>  /* not correct */
>  if ( xxx )
>      if ( yyy )
>          something;
> 
> So basically we would keep the { } here but we would skip them ...

Ok this clarifies a lot, thank you, I will check the code and I will fix it where it’s not
compliant.

> 
>> +#ifdef CONFIG_HAS_DEVICE_TREE
>> +void btcpupools_dtb_parse(void);
>> +#else
>> +static inline void btcpupools_dtb_parse(void) {}
>> +#endif
> 
> same comment about !CONFIG_HAS_DEVICE_TREE

Yes I will fix it in the next serie.

Cheers,
Luca