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Re: [PATCH] Add TUNABLES to control IFUNC selection and cache sizes
- From: Siddhesh Poyarekar <siddhesh at gotplt dot org>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Cc: Erich Elsen <eriche at google dot com>
- Date: Fri, 9 Jun 2017 11:15:56 +0530
- Subject: Re: [PATCH] Add TUNABLES to control IFUNC selection and cache sizes
- Authentication-results: sourceware.org; auth=none
- References: <20170608200335.GA30996@gmail.com>
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