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Subject: Re: [PATCH v2 1/3] Tunables: Add tunables of spin count for pthread
 adaptive spin mutex
To: Kemi Wang <kemi.wang@intel.com>,
 Adhemerval Zanella <adhemerval.zanella@linaro.org>,
 Glibc alpha <libc-alpha@sourceware.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>, Tim Chen
 <tim.c.chen@intel.com>, Andi Kleen <andi.kleen@intel.com>,
 Ying Huang <ying.huang@intel.com>, Aaron Lu <aaron.lu@intel.com>,
 Lu Aubrey <aubrey.li@intel.com>
References: <1524624988-29141-1-git-send-email-kemi.wang@intel.com>
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <0c66f19d-c0e8-accd-85dd-7e55dd6da1af@redhat.com>
Date: Wed, 02 May 2018 08:04:00 -0000
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On 04/25/2018 04:56 AM, Kemi Wang wrote:

> +  mutex {
> +    spin_count {
> +      type: INT_32
> +      minval: 0
> +      maxval: 30000
> +      default: 1000
> +    }

How did you come up with the default and maximum values?  Larger maximum 
values might be useful for testing boundary conditions.

> +# define TUNABLE_CALLBACK_FNDECL(__name, __type)			\
> +static inline void						\
> +__always_inline							\
> +do_set_mutex_ ## __name (__type value)			\
> +{								\
> +  __mutex_aconf.__name = value;				\
> +}								\
> +void								\
> +TUNABLE_CALLBACK (set_mutex_ ## __name) (tunable_val_t *valp) \
> +{								\
> +  __type value = (__type) (valp)->numval;			\
> +  do_set_mutex_ ## __name (value);				\
> +}
> +
> +TUNABLE_CALLBACK_FNDECL (spin_count, int32_t);

I'm not sure if the macro is helpful in this context.

> +static void
> +mutex_tunables_init (int argc __attribute__ ((unused)),
> +			      char **argv  __attribute__ ((unused)),
> +					      char **environ)
> +{
> +#if HAVE_TUNABLES
> +
> +  TUNABLE_GET (spin_count, int32_t,
> +		  TUNABLE_CALLBACK (set_mutex_spin_count));
> +#endif
> +}
> +
> +#ifdef SHARED
> +# define INIT_SECTION ".init_array"
> +#else
> +# define INIT_SECTION ".preinit_array"
> +#endif
> +
> +void (*const __pthread_mutex_tunables_init_array []) (int, char **, char **)
> +  __attribute__ ((section (INIT_SECTION), aligned (sizeof (void *)))) =
> +{
> +  &mutex_tunables_init
> +};

Can't you perform the initialization as part of overall pthread 
initialization?  This would avoid the extra relocation.

Thanks,
Florian