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

* Mike Travis <travis@sgi.com> 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


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