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

[Siddhesh Poyarekar]

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