[RFC][PATCH] tunables: Add elision tunable

[Stefan Liebler]

On 11/16/2017 07:44 PM, Rogerio Alves wrote:
> Hi Carlos,
> 
> All documentation suggestions was made on patch v5. Thanks for the review.
> 
> Regards
> 
> Rogerio.
> 

Hi 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!

Bye.
Stefan
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