Re: [PATCH 4/5] x86: Add config variables for SMP_MAX

[Mike Travis]

Ingo Molnar wrote:
> * Mike Travis <travis@xxxxxxx> wrote:
> 
>>>> +config THREAD_ORDER
>>>> +	int "Kernel stack size (in page order)"
>>>> +	range 1 3
>>>> +	depends on X86_64_SMP
>>>> +	default "3" if X86_SMP_MAX
>>>> +	default "1"
>>>> +	help
>>>> +	  Increases kernel stack size.
>>>> +
>>> Could you please elaborate, why this is needed and put more info 
>>> about this requirement into this patch description?
>>>
>>> People worked hard to push data allocation from stack to heap to 
>>> make THREAD_ORDER of 0 and 1 possible. So why increase it again and 
>>> why does this help scalability?
>>>
>>> Many thanks and Best Regards
>>>
>>> Ingo Oeser, puzzled a bit :-)
>>
>> The primary problem arises because of cpumask_t local variables.  
>> Until I can deal with these, increasing NR_CPUS to a really large 
>> value increases stack size dramatically.
> 
> those should be fixed:
> 
>> Here are the top stack consumers with NR_CPUS = 4k.
>>
>>                          16392 isolated_cpu_setup
>>                          10328 build_sched_domains
>>                           8248 numa_initmem_init
>>                           4664 cpu_attach_domain
>>                           4104 show_shared_cpu_map
>>                           3656 centrino_target
>>                           3608 powernowk8_cpu_init
>>                           3192 sched_domain_node_span
>>                           3144 acpi_cpufreq_target
>>                           2584 __svc_create_thread
>>                           2568 cpu_idle_wait
>>                           2136 netxen_nic_flash_print
>>                           2104 powernowk8_target
>>                           2088 _cpu_down
>>                           2072 cache_add_dev
>>                           2056 get_cur_freq
>>                              0 acpi_processor_ffh_cstate_probe
>>                           2056 microcode_write
>>                              0 acpi_processor_get_throttling
>>                           2048 check_supported_cpu
> 
> (and most of that is performance-uncritical.)
> 
> 	Ingo

How big is the stack during early startup?

Thanks,
Mike
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