lowlevellock.c for arm differs from the generic lowlevellock.c only in
insignificant ways, so can be removed. Happily, this fixes BZ 15119
(unnecessary busy loop in __lll_timedlock_wait on arm).
The notable differences between the arm and generic implementations are:
1) arm __lll_timedlock_wait has a fast path out if futex has been set
to 0 between since the function was called. This seems unlikely to
happen very often, so it seems at worst harmless to lose this fast
path.
2) Some function in arm's lowlevellock.c set futex to 2 if it was 1.
The generic version always sets the futex to 2. As futex can only be
0, 1 or 2 on entry into these functions, the behaviour is equivalent.
(If the futex manages to be 0 on entry then we've just lost another
unlikely fast path out.)
There are no test suite regressions.
Note that hppa and sparc also have their own lowlevellock.c. I believe
hppa can also be removed, so I'll send a separate patch for that
shortly. sparc's seems to be genuinely needed as it uses a different
locking structure.
Also note that the analysis at
https://sourceware.org/ml/libc-ports/2013-02/msg00021.html indicates a
further locking performance bug to fix - I've got a partial patch for
that which I can submit once I've finished testing.
2014-05-01 Bernard Ogden <bernie.ogden@linaro.org>
[BZ #15119]
* sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c: Remove file.
[BZ #15215] This unifies various pthread_once architecture-specific
implementations which were using the same algorithm with slightly different
implementations. It also adds missing memory barriers that are required for
correctness.
This patch moves the __PTHREAD_SPINS definition to arch specific header
since pthread_mutex_t layout is also arch specific. This leads to no
need to defining __PTHREAD_MUTEX_HAVE_ELISION and thus removing of the
undefined compiler warning.
I've moved the ARM port from ports to the main sysdeps hierarchy.
Beyond the README update, the move of the files was simply
git mv ports/sysdeps/arm sysdeps/arm
git mv ports/sysdeps/unix/arm sysdeps/unix/arm
git mv ports/sysdeps/unix/sysv/linux/arm sysdeps/unix/sysv/linux/arm
and in addition to the ChangeLog entries here, I put a note at the top
of ports/ChangeLog.arm similar to that at the top of
ChangeLog.powerpc. There is deliberately no NEWS change, as I think
it makes the most sense to put in a general note above all ports
having moved if we can achieve that for 2.20.
Tested that disassembly of installed shared libraries for arm is the
same before and after this patch, except for data (not instructions)
in ld.so (there are assertions in sysdeps/arm/dl-machine.h, and the
path by which that file is found, and so by which it appears in the
assertion message, changes as a result of the move).
* sysdeps/arm: Move directory from ports/sysdeps/arm.
* sysdeps/unix/arm: Move directory from ports/sysdeps/unix/arm.
* sysdeps/unix/sysv/linux/arm: Move directory from
ports/sysdeps/unix/sysv/linux/arm.
* README: Update listing for arm-*-linux-gnueabi.
ports/ChangeLog.arm:
* sysdeps/arm: Move directory to ../sysdeps/arm.
* sysdeps/unix/arm: Move directory to ../sysdeps.arm.
* sysdeps/unix/sysv/linux/arm: Move directory to
../sysdeps/unix/sysv/linux/arm.
