linux-kernel - Re: [RFC 2/6] sched: add a new SD SHARE_POWERLINE flag for sched

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Message-ID: <50939FFE.9020401@ti.com>
Date:	Fri, 2 Nov 2012 15:57:10 +0530
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linaro-dev@...ts.linaro.org>, <peterz@...radead.org>,
	<mingo@...hat.com>, <pjt@...gle.com>, <linux@....linux.org.uk>
Subject: Re: [RFC 2/6] sched: add a new SD SHARE_POWERLINE flag for sched_domain

On Monday 29 October 2012 03:20 PM, Vincent Guittot wrote:
>   It looks like i need to describe more what
>
> On 29 October 2012 10:40, Vincent Guittot <vincent.guittot@...aro.org> wrote:
>> On 24 October 2012 17:17, Santosh Shilimkar <santosh.shilimkar@...com> wrote:
>>> Vincent,
>>>
>>> Few comments/questions.
>>>
>>>
>>> On Sunday 07 October 2012 01:13 PM, Vincent Guittot wrote:
>>>>
>>>> This new flag SD SHARE_POWERLINE reflects the sharing of the power rail
>>>> between the members of a domain. As this is the current assumption of the
>>>> scheduler, the flag is added to all sched_domain
>>>>
>>>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>>>> ---
>>>>    arch/ia64/include/asm/topology.h |    1 +
>>>>    arch/tile/include/asm/topology.h |    1 +
>>>>    include/linux/sched.h            |    1 +
>>>>    include/linux/topology.h         |    3 +++
>>>>    kernel/sched/core.c              |    5 +++++
>>>>    5 files changed, 11 insertions(+)
>>>>
>>>> diff --git a/arch/ia64/include/asm/topology.h
>>>> b/arch/ia64/include/asm/topology.h
>>>> index a2496e4..065c720 100644
>>>> --- a/arch/ia64/include/asm/topology.h
>>>> +++ b/arch/ia64/include/asm/topology.h
>>>> @@ -65,6 +65,7 @@ void build_cpu_to_node_map(void);
>>>>                                  | SD_BALANCE_EXEC       \
>>>>                                  | SD_BALANCE_FORK       \
>>>>                                  | SD_WAKE_AFFINE,       \
>>>> +                               | arch_sd_share_power_line()            \
>>>>          .last_balance           = jiffies,              \
>>>>          .balance_interval       = 1,                    \
>>>>          .nr_balance_failed      = 0,                    \
>>>> diff --git a/arch/tile/include/asm/topology.h
>>>> b/arch/tile/include/asm/topology.h
>>>> index 7a7ce39..d39ed0b 100644
>>>> --- a/arch/tile/include/asm/topology.h
>>>> +++ b/arch/tile/include/asm/topology.h
>>>> @@ -72,6 +72,7 @@ static inline const struct cpumask *cpumask_of_node(int
>>>> node)
>>>>                                  | 0*SD_PREFER_LOCAL                     \
>>>>                                  | 0*SD_SHARE_CPUPOWER                   \
>>>>                                  | 0*SD_SHARE_PKG_RESOURCES              \
>>>> +                               | arch_sd_share_power_line()            \
>>>>                                  | 0*SD_SERIALIZE                        \
>>>>                                  ,                                       \
>>>>          .last_balance           = jiffies,                              \
>>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>>> index 4786b20..74f2daf 100644
>>>> --- a/include/linux/sched.h
>>>> +++ b/include/linux/sched.h
>>>> @@ -862,6 +862,7 @@ enum cpu_idle_type {
>>>>    #define SD_WAKE_AFFINE                0x0020  /* Wake task to waking CPU
>>>> */
>>>>    #define SD_PREFER_LOCAL               0x0040  /* Prefer to keep tasks
>>>> local to this domain */
>>>>    #define SD_SHARE_CPUPOWER     0x0080  /* Domain members share cpu power
>>>> */
>>>> +#define SD_SHARE_POWERLINE     0x0100  /* Domain members share power
>>>> domain */
>>>
>>> If you ignore the current use of SD_SHARE_CPUPOWER, isn't the meaning of
>>> CPUPOWER and POWERLINE is same here. Just trying to understand the clear
>>> meaning of this new flag. Have you not considered SD_SHARE_CPUPOWER
>>> because it is being used for cpu_power and needs at least minimum two
>>> domains ? SD_PACKING would have been probably more appropriate based
>>> on the way it is being used in further series.
>>
>> CPUPOWER reflects the share of hw ressources between cores like for
>> hyper threading. POWERLINE describes the fact that cores are sharing
>> the same power line amore precisely the powergate.
>
> Sorry, the mail has been sent too early while I was writing it
>
> CPUPOWER reflects the share of hw ressources between cores like for
> hyper threading. POWERLINE describes the fact that cores are sharing
> the same power line and more precisely the same power gating. It looks
> like I need to describe more precisely what i would mean with
> SHARE_POWERLINE.
>
Yes. More description will help. I see bit of overlap POWERLINE
flag with SD_SHARE_CPUPOWER and SD_SHARE_PKG_RESOURCES and hence
the questions.


> I don't want to use PACKING because it's more a behavior than a
> feature. If cores can power gate independently (!SD_SHARE_POWERLINE),
> packing small tasks is one interesting behavior but it may be not the
> only one. I want to make a difference between the HW configuration and
> the behavior we want to have above it
>
Fair enough. Thanks for clarification.

Regards,
Santosh


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