Re: [RFC PATCH 07/16 v3] Init Workload Consolidation flags in sched_domain

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

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On 03/06/14 13:14, Peter Zijlstra wrote:
> On Fri, May 30, 2014 at 02:36:03PM +0800, Yuyang Du wrote:
>> Workload Consolidation can be enabled/disabled on the fly. This patchset
>> enables MC and CPU domain WC by default.
>>
>> To enable CPU WC (SD_WORKLOAD_CONSOLIDATION=0x8000):
>>
>> sysctl -w kernel.sched_domain.cpuX.domainY.flags += 0x8000
>>
>> To disable CPU WC:
>>
>> sysctl -w kernel.sched_domain.cpuX.domainY.flags -= 0x8000
>>
>> Signed-off-by: Yuyang Du <yuyang.du@intel.com>
>> ---
>>  include/linux/topology.h |    6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/include/linux/topology.h b/include/linux/topology.h
>> index 7062330..ebc339c3 100644
>> --- a/include/linux/topology.h
>> +++ b/include/linux/topology.h
>> @@ -102,12 +102,14 @@ int arch_update_cpu_topology(void);
>>  				| 0*SD_SERIALIZE			\
>>  				| 0*SD_PREFER_SIBLING			\
>>  				| arch_sd_sibling_asym_packing()	\
>> +				| 0*SD_WORKLOAD_CONSOLIDATION	\
>>  				,					\
>>  	.last_balance		= jiffies,				\
>>  	.balance_interval	= 1,					\
>>  	.smt_gain		= 1178,	/* 15% */			\
>>  	.max_newidle_lb_cost	= 0,					\
>>  	.next_decay_max_lb_cost	= jiffies,				\
>> +	.consolidating_coeff = 0,					\
>>  }
>>  #endif
>>  #endif /* CONFIG_SCHED_SMT */
>> @@ -134,11 +136,13 @@ int arch_update_cpu_topology(void);
>>  				| 0*SD_SHARE_CPUPOWER			\
>>  				| 1*SD_SHARE_PKG_RESOURCES		\
>>  				| 0*SD_SERIALIZE			\
>> +				| 1*SD_WORKLOAD_CONSOLIDATION	\
>>  				,					\
>>  	.last_balance		= jiffies,				\
>>  	.balance_interval	= 1,					\
>>  	.max_newidle_lb_cost	= 0,					\
>>  	.next_decay_max_lb_cost	= jiffies,				\
>> +	.consolidating_coeff = 180,					\
>>  }
>>  #endif
>>  #endif /* CONFIG_SCHED_MC */
>> @@ -167,11 +171,13 @@ int arch_update_cpu_topology(void);
>>  				| 0*SD_SHARE_PKG_RESOURCES		\
>>  				| 0*SD_SERIALIZE			\
>>  				| 1*SD_PREFER_SIBLING			\
>> +				| 1*SD_WORKLOAD_CONSOLIDATION	\
>>  				,					\
>>  	.last_balance		= jiffies,				\
>>  	.balance_interval	= 1,					\
>>  	.max_newidle_lb_cost	= 0,					\
>>  	.next_decay_max_lb_cost	= jiffies,				\
>> +	.consolidating_coeff = 180,					\
>>  }
>>  #endif
> 
> What tree are you working against, non of that exists anymore. Also, you
> cannot unconditionally set this.
> 

Hi Yuyang,

I'm running these patches on my ARM TC2 on top of
kernel/git/torvalds/linux.git (v3.15-rc7-79-gfe45736f4134). There're
considerable changes in the area of sched domain setup since Vincent's
patchset 'rework sched_domain topology description' (destined for v3.16)
which you can find on kernel/git/tip/tip.git .

Why did you make SD_WORKLOAD_CONSOLIDATION controllable via sysctl? All
the other SD flags are set during setup. Your top_flag_domain() function
takes care of figuring out what is the highest sd level this is set on
during load-balance but I can't find any good reason to do it this way
other then for testing purposes?

Setting SD_WORKLOAD_CONSOLIDATION  (which is probably a behavioural flag
rather than a topology description related one) on a certain sd level
requires you to also think about its implications in sd_init() and in sd
degenerate functionality.

-- Dietmar