diff options
| -rw-r--r-- | libitm/ChangeLog | 6 | ||||
| -rw-r--r-- | libitm/method-gl.cc | 33 |
2 files changed, 11 insertions, 28 deletions
diff --git a/libitm/ChangeLog b/libitm/ChangeLog index 0a06bfec7f4..977613d05be 100644 --- a/libitm/ChangeLog +++ b/libitm/ChangeLog @@ -1,5 +1,11 @@ 2012-02-20 Torvald Riegel <triegel@redhat.com> + * method-gl.cc (gl_wt_dispatch::trycommit): Remove handling of + serial mode corner cases made obsolete by prior gtm_rwlock changes. + (gl_wt_dispatch.rollback): Same. + +2012-02-20 Torvald Riegel <triegel@redhat.com> + * method-gl.cc (gl_wt_dispatch::pre_write): Optimize memory orders. 2012-02-20 Torvald Riegel <triegel@redhat.com> diff --git a/libitm/method-gl.cc b/libitm/method-gl.cc index 503c19e5921..5bae22b90c1 100644 --- a/libitm/method-gl.cc +++ b/libitm/method-gl.cc @@ -76,12 +76,10 @@ static gl_mg o_gl_mg; // validate that no other update transaction comitted before we acquired the // orec, so we have the most recent timestamp and no other transaction can // commit until we have committed). -// However, we therefore cannot use this method for a serial transaction -// (because shared_state needs to remain at ~0) and we have to be careful -// when switching to serial mode (see the special handling in trycommit() and -// rollback()). -// ??? This sharing adds some complexity wrt. serial mode. Just use a separate -// state variable? +// However, we therefore depend on shared_state not being modified by the +// serial lock during upgrades to serial mode, which is ensured by +// gtm_thread::serialirr_mode by not calling gtm_rwlock::write_upgrade_finish +// before we have committed or rolled back. class gl_wt_dispatch : public abi_dispatch { protected: @@ -283,15 +281,6 @@ public: gtm_thread* tx = gtm_thr(); gtm_word v = tx->shared_state.load(memory_order_relaxed); - // Special case: If shared_state is ~0, then we have acquired the - // serial lock (tx->state is not updated yet). In this case, the previous - // value isn't available anymore, so grab it from the global lock, which - // must have a meaningful value because no other transactions are active - // anymore. In particular, if it is locked, then we are an update - // transaction, which is all we care about for commit. - if (v == ~(typeof v)0) - v = o_gl_mg.orec.load(memory_order_relaxed); - // Release the orec but do not reset shared_state, which will be modified // by the serial lock right after our commit anyway. Also, resetting // shared state here would interfere with the serial lock's use of this @@ -319,15 +308,6 @@ public: gtm_thread *tx = gtm_thr(); gtm_word v = tx->shared_state.load(memory_order_relaxed); - // Special case: If shared_state is ~0, then we have acquired the - // serial lock (tx->state is not updated yet). In this case, the previous - // value isn't available anymore, so grab it from the global lock, which - // must have a meaningful value because no other transactions are active - // anymore. In particular, if it is locked, then we are an update - // transaction, which is all we care about for rollback. - bool is_serial = v == ~(typeof v)0; - if (is_serial) - v = o_gl_mg.orec.load(memory_order_relaxed); // Release lock and increment version number to prevent dirty reads. // Also reset shared state here, so that begin_or_restart() can expect a @@ -340,10 +320,7 @@ public: o_gl_mg.orec.store(v, memory_order_release); // Also reset the timestamp published via shared_state. - // Special case: Only do this if we are not a serial transaction - // because otherwise, we would interfere with the serial lock. - if (!is_serial) - tx->shared_state.store(v, memory_order_release); + tx->shared_state.store(v, memory_order_release); // We need a store-load barrier after this store to prevent it // from becoming visible after later data loads because the |