diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/powerpc/elision-conf.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/elision-conf.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c index 906882a..fc82bd1 100644 --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c @@ -127,6 +127,26 @@ elision_init (int argc __attribute__ ((unused)), TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort)); #endif + /* Linux from 3.9 through 4.2 do not abort HTM transaction on syscalls, + instead it suspends the transaction and resumes it when returning to + usercode. The side-effects of the syscall will always remain visible, + even if the transaction is aborted. This is an issue when a transaction + is used along with futex syscall, on pthread_cond_wait for instance, + where futex might succeed but the transaction is rolled back leading + the condition variable object in an inconsistent state. + + Glibc used to prevent it by always aborting a transaction before issuing + a syscall. Linux 4.2 also decided to abort active transaction in + syscalls which makes the glibc workaround superflours. Worse, glibc + transaction abortions leads to a performance issues on recent kernels. + + So Lock Elision is just enabled when it has been explict set (either + by tunables of by a configure switch) and if kernel aborts HTM + transactions on syscalls (PPC_FEATURE2_HTM_NOSC) */ + + __pthread_force_elision = (__pthread_force_elision + && GLRO (dl_hwcap2) & PPC_FEATURE2_HTM_NOSC); + if (!__pthread_force_elision) __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks. */ } |