Re: [PATCH v2 5/7] sched: add a new SD_SHARE_POWERDOMAIN for sched_domain

[Vincent Guittot]

On 19 March 2014 12:05, Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx> wrote:
> On 03/19/2014 03:22 PM, Vincent Guittot wrote:
>> On 19 March 2014 07:21, Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx> wrote:
>>> Hi Vincent,
>>>
>>> On 03/18/2014 11:26 PM, Vincent Guittot wrote:
>>>> A new flag SD_SHARE_POWERDOMAIN is created to reflect whether groups of CPUs
>>>> in a sched_domain level can or not reach different power state. As an example,
>>>> the flag should be cleared at CPU level if groups of cores can be power gated
>>>> independently. This information can be used to add load balancing level between
>>>> group of CPUs than can power gate independantly. The default behavior of the
>>>> scheduler is to spread tasks across CPUs and groups of CPUs so the flag is set
>>>> into all sched_domains.
>>>
>>> I don't see this flag being set either in sd_init() or in
>>> default_topology[]. Should not the default_topology[] flag setting
>>> routines set this flag at every level of sched domain along with other
>>> topology flags, unless the arch wants to override it?
>>
>> Hi Preeti
>>
>> I have made the choice to not add it in the default table for the
>> moment because the scheduler behavior is not changed. It will be added
>> with patchset that will take advantage of this flag in the load
>> balance decision.
>
> Ok if you are looking at setting this flag in the default topology table
> then [patch 7/7]:sched: powerpc: Add SD_SHARE_POWERDOMAIN for SMT level
> looks good to me. Please add my Reviewed-by to this patch.
>
> However if you are looking at initializing this flag as being set by
> default in sd_init() then the archs will have to revert the flag, rather
> than set it in their respective topology tables for the sched domains
> which have their groups power gated. In which case the    [patch 7/7]
> would be incorrect.
>    But wait, I see that you  mention that the topology level flags are
> left to the archs to set if required. So I am assuming you will not set
> the SD_SHARE_POWER_DOMAIN flag in sd_init() right?

Yes, it will not be set in sd_init but with the function pointer of the table

Vincent

>
> Regards
> Preeti U Murthy
>>
>> Regards,
>> Vincent
>>
>>>
>>> Regards
>>> Preeti U Murthy
>>>> This flag is part of the topology flags that can be set by arch.
>>>>
>>>> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>>>> ---
>>>>  include/linux/sched.h | 1 +
>>>>  kernel/sched/core.c   | 9 ++++++---
>>>>  2 files changed, 7 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>>> index 6479de4..7048369 100644
>>>> --- a/include/linux/sched.h
>>>> +++ b/include/linux/sched.h
>>>> @@ -861,6 +861,7 @@ enum cpu_idle_type {
>>>>  #define SD_BALANCE_WAKE              0x0010  /* Balance on wakeup */
>>>>  #define SD_WAKE_AFFINE               0x0020  /* Wake task to waking CPU */
>>>>  #define SD_SHARE_CPUPOWER    0x0080  /* Domain members share cpu power */
>>>> +#define SD_SHARE_POWERDOMAIN 0x0100  /* Domain members share power domain */
>>>>  #define SD_SHARE_PKG_RESOURCES       0x0200  /* Domain members share cpu pkg resources */
>>>>  #define SD_SERIALIZE         0x0400  /* Only a single load balancing instance */
>>>>  #define SD_ASYM_PACKING              0x0800  /* Place busy groups earlier in the domain */
>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>>> index 0b51ee3..224ec3b 100644
>>>> --- a/kernel/sched/core.c
>>>> +++ b/kernel/sched/core.c
>>>> @@ -5298,7 +5298,8 @@ static int sd_degenerate(struct sched_domain *sd)
>>>>                        SD_BALANCE_FORK |
>>>>                        SD_BALANCE_EXEC |
>>>>                        SD_SHARE_CPUPOWER |
>>>> -                      SD_SHARE_PKG_RESOURCES)) {
>>>> +                      SD_SHARE_PKG_RESOURCES |
>>>> +                      SD_SHARE_POWERDOMAIN)) {
>>>>               if (sd->groups != sd->groups->next)
>>>>                       return 0;
>>>>       }
>>>> @@ -5329,7 +5330,8 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
>>>>                               SD_BALANCE_EXEC |
>>>>                               SD_SHARE_CPUPOWER |
>>>>                               SD_SHARE_PKG_RESOURCES |
>>>> -                             SD_PREFER_SIBLING);
>>>> +                             SD_PREFER_SIBLING |
>>>> +                             SD_SHARE_POWERDOMAIN);
>>>>               if (nr_node_ids == 1)
>>>>                       pflags &= ~SD_SERIALIZE;
>>>>       }
>>>> @@ -5946,7 +5948,8 @@ static int sched_domains_curr_level;
>>>>       (SD_SHARE_CPUPOWER |            \
>>>>        SD_SHARE_PKG_RESOURCES |       \
>>>>        SD_NUMA |                      \
>>>> -      SD_ASYM_PACKING)
>>>> +      SD_ASYM_PACKING |              \
>>>> +      SD_SHARE_POWERDOMAIN)
>>>>
>>>>  static struct sched_domain *
>>>>  sd_init(struct sched_domain_topology_level *tl, int cpu)
>>>>
>>>
>>
>
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