[RFC][PATCH] tunables: Add elision tunable

[Tulio Magno Quites Machado Filho]

Stefan Liebler <stli@linux.vnet.ibm.com> writes:

> On 11/16/2017 07:44 PM, Rogerio Alves wrote:
>> All documentation suggestions was made on patch v5. Thanks for the review.
>> 
>> Regards
>> 
>> Rogerio.
>> 
>
> I've applied your patch in order to test it on s390.
> Unfortunately building glibc is now failing.
>
> Here are some notes:
>
> git apply warned:
> 0001-Add-elision-tunables.patch:291: trailing whitespace.
> # Disable elision for tst-mutex8 so it can verify error case for
> warning: 1 line adds whitespace errors.
>
> Changing configure.ac is not sufficient.
> Please regenerate configure in order to reflect the changes in configure.ac.
>
> There are also usages of enable_lock_elision and ENABLE_LOCK_ELISION in 
> config.make.in, sysdeps/unix/sysv/linux/s390/Makefile, 
> sysdeps/s390/nptl/bits/pthreadtypes-arch.h, sysdeps/s390/configure.ac.
>
> Please have a look into attached diff which applies on top of your patch 
> v5. With those changes I was able to build glibc on s390.
>
> Afterwards I've run a small test program which determines if 
> pthread_mutex_lock is using a transaction or not:
>
> ./prog
> Lock was a normal lock!
>
> GLIBC_TUNABLES=glibc.elision.enable=1 ./prog
> Lock was elided via a transaction! (nesting-depth=1)
>
> GLIBC_TUNABLES=glibc.elision.enable=0 ./prog
> Lock was a normal lock!
>
> chmod +s prog_secure
> GLIBC_TUNABLES=glibc.elision.enable=1 ./prog_secure
> Lock was a normal lock!

I applied this patch, updated the ChangeLog, run tests on ppc{|64|64le},
s390x and x86_64, and pushed the patch as 07ed18d26a342.

Thanks!

-- 
Tulio Magno