Re: [PATCH 0/2] Make tunable a default feature

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 14/03/23 15:02, Siddhesh Poyarekar wrote:
> On 2023-03-13 15:06, Adhemerval Zanella wrote:
>> It is enabled as default since 2.26, some features option require it
>> (such as hwcap mask, huge pages support, and lock elisition tuning),
>> and assuming its support also simplifies the build permutation.
> 
> from a historical perspective, there was not just the question of enabling tunables but also providing multiple ways to read tunables, each having its own parser.  That is why there's a 'valstring' as an option for --enable-tunables.

Does it really make sense to provide such option, where multiple distributions
would support different tunables? I don't this much as way forward, it would require
additional effort to document, along with some prudence to make it concise. And
its has the inherent problem of fragmentation.

> 
> Over the years there haven't really been any other ideas to read tunables.  There's the idea of systemwide tunables through, e.g. ld.so.conf that we'd like to have at some point, but that is more effective alongside valstring than as an either-or feature.

For ld.so cache, the program can use DF_1_NODEFLIB to either avoid its costs or
not use system cache (if its uses RUNPATH).  I think a system-wide tunable would
require a similar scheme, where the program can opt-out if required.

> 
> There's also conceivably a use case for having only systemwide tunables without any valstring override but maybe that should get supported when it's actually needed by someone.  So in summary, I'm not aware of anybody using --disable-tunables, so I'm not opposed to removing the configure flag altogether and simplifying the code.  Hopefully if someone is using it they'll come forward before this patchset gets accepted.

Alright, so I think it should be good to setup this for next release then.