[PATCH] Add TUNABLES to control IFUNC selection and cache sizes

[H.J. Lu]

On Thu, Jun 8, 2017 at 10:45 PM, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> On Friday 09 June 2017 01:33 AM, H.J. Lu wrote:
>> The current IFUNC selection is based on microbenchmarks in glibc.  It
>> should give the best performance for most workloads.  But other choices
>> may have better performance for a particular workload or on the hardware
>> which wasn't available at the selection was made.  The environment
>> variable, GLIBC_IFUNC=-xxx,yyy,-zzz...., can be used to enable CPU/ARCH
>> feature yyy, disable CPU/ARCH feature yyy and zzz, where the feature
>> name is case-sensitive and has to match the ones in cpu-features.h.  It
>> can be used by glibc developers to override the IFUNC selection to tune
>> for a new processor or improve performance for a particular workload.
>> It isn't intended for normal end users.
>
> We have agreed in the past that env_alias is only a compatibility hack
> to allow existing environment variables to be ported into tunables so
> please don't add new ones.  glibc.tune.ifunc should be the only way to
> select ifuncs.
>
> Siddhesh

Does that mean tunables must be enabled to use it? Will tunables
be enabled by default?

-- 
H.J.