A single environment variable for tunables vs a variable per tunable

[Siddhesh Poyarekar <sid at reserved-bit dot com>]

On Thu, 2015-09-17 at 10:51 -0700, Roland McGrath wrote:
> There should be no explicit code using new environment variables at
> all.
> It should all go through the tunables framework so policy and
> knowledge
> about use of environment variables is centralized.

I pushed some code to the siddhesh/tunables branch last week that reads
just one magic environment variable and parses the string to initialize
all tunables at once.  This gives a definite path to deprecate the
existing arbitrary environment variables in future as well since it
clearly separates those bits from the core framework.  So now y'all
have both approaches to try out while I cool my heels off for a bit - I
hope to be back hacking soon.

We have talked about both approaches for a bit in different threads and
I continue to have a slight preference for the single environment
variable for the sheer ease of initialization and the possibility of
doing it really early once I figure out how to get the code included
into the dynamic linker without dropping it into the elf directory. 
 All other differences seem cosmetic to me.

Siddhesh