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Diffstat (limited to 'libitm/retry.cc')
| -rw-r--r-- | libitm/retry.cc | 265 |
1 files changed, 265 insertions, 0 deletions
diff --git a/libitm/retry.cc b/libitm/retry.cc new file mode 100644 index 00000000000..decd7731b46 --- /dev/null +++ b/libitm/retry.cc @@ -0,0 +1,265 @@ +/* Copyright (C) 2008, 2009, 2011 Free Software Foundation, Inc. + Contributed by Richard Henderson <rth@redhat.com>. + + This file is part of the GNU Transactional Memory Library (libitm). + + Libitm is free software; you can redistribute it and/or modify it + under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + Libitm is distributed in the hope that it will be useful, but WITHOUT ANY + WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS + FOR A PARTICULAR PURPOSE. See the GNU General Public License for + more details. + + Under Section 7 of GPL version 3, you are granted additional + permissions described in the GCC Runtime Library Exception, version + 3.1, as published by the Free Software Foundation. + + You should have received a copy of the GNU General Public License and + a copy of the GCC Runtime Library Exception along with this program; + see the files COPYING3 and COPYING.RUNTIME respectively. If not, see + <http://www.gnu.org/licenses/>. */ + +#include <stdlib.h> +#include <string.h> +#include <ctype.h> +#include "libitm_i.h" + +// The default TM method used when starting a new transaction. +static GTM::abi_dispatch* default_dispatch = 0; +// The default TM method as requested by the user, if any. +static GTM::abi_dispatch* default_dispatch_user = 0; + +void +GTM::gtm_thread::decide_retry_strategy (gtm_restart_reason r) +{ + struct abi_dispatch *disp = abi_disp (); + + this->restart_reason[r]++; + this->restart_total++; + + if (r == RESTART_INIT_METHOD_GROUP) + { + // A re-initializations of the method group has been requested. Switch + // to serial mode, initialize, and resume normal operation. + if ((state & STATE_SERIAL) == 0) + { + // We have to eventually re-init the method group. Therefore, + // we cannot just upgrade to a write lock here because this could + // fail forever when other transactions execute in serial mode. + // However, giving up the read lock then means that a change of the + // method group could happen in-between, so check that we're not + // re-initializing without a need. + // ??? Note that we can still re-initialize too often, but avoiding + // that would increase code complexity, which seems unnecessary + // given that re-inits should be very infrequent. + serial_lock.read_unlock(this); + serial_lock.write_lock(); + if (disp->get_method_group() == default_dispatch->get_method_group()) + { + // Still the same method group. + disp->get_method_group()->fini(); + disp->get_method_group()->init(); + } + serial_lock.write_unlock(); + serial_lock.read_lock(this); + if (disp->get_method_group() != default_dispatch->get_method_group()) + { + disp = default_dispatch; + set_abi_disp(disp); + } + } + else + { + // We are a serial transaction already, which makes things simple. + disp->get_method_group()->fini(); + disp->get_method_group()->init(); + } + } + + bool retry_irr = (r == RESTART_SERIAL_IRR); + bool retry_serial = (retry_irr || this->restart_total > 100); + + // We assume closed nesting to be infrequently required, so just use + // dispatch_serial (with undo logging) if required. + if (r == RESTART_CLOSED_NESTING) + retry_serial = true; + + if (retry_serial) + { + // In serialirr_mode we can succeed with the upgrade to + // write-lock but fail the trycommit. In any case, if the + // write lock is not yet held, grab it. Don't do this with + // an upgrade, since we've no need to preserve the state we + // acquired with the read. + // Note that we will be restarting with either dispatch_serial or + // dispatch_serialirr, which are compatible with all TM methods; if + // we would retry with a different method, we would have to first check + // whether the default dispatch or the method group have changed. Also, + // the caller must have rolled back the previous transaction, so we + // don't have to worry about things such as privatization. + if ((this->state & STATE_SERIAL) == 0) + { + this->state |= STATE_SERIAL; + serial_lock.read_unlock (this); + serial_lock.write_lock (); + } + + // We can retry with dispatch_serialirr if the transaction + // doesn't contain an abort and if we don't need closed nesting. + if ((this->prop & pr_hasNoAbort) && (r != RESTART_CLOSED_NESTING)) + retry_irr = true; + } + + // Note that we can just use serial mode here without having to switch + // TM method sets because serial mode is compatible with all of them. + if (retry_irr) + { + this->state = (STATE_SERIAL | STATE_IRREVOCABLE); + disp = dispatch_serialirr (); + set_abi_disp (disp); + } + else if (retry_serial) + { + disp = dispatch_serial(); + set_abi_disp (disp); + } +} + + +// Decides which TM method should be used on the first attempt to run this +// transaction. +GTM::abi_dispatch* +GTM::gtm_thread::decide_begin_dispatch (uint32_t prop) +{ + // TODO Pay more attention to prop flags (eg, *omitted) when selecting + // dispatch. + if ((prop & pr_doesGoIrrevocable) || !(prop & pr_instrumentedCode)) + return dispatch_serialirr(); + + // If we might need closed nesting and the default dispatch has an + // alternative that supports closed nesting, use it. + // ??? We could choose another TM method that we know supports closed + // nesting but isn't the default (e.g., dispatch_serial()). However, we + // assume that aborts that need closed nesting are infrequent, so don't + // choose a non-default method until we have to actually restart the + // transaction. + if (!(prop & pr_hasNoAbort) && !default_dispatch->closed_nesting() + && default_dispatch->closed_nesting_alternative()) + return default_dispatch->closed_nesting_alternative(); + + // No special case, just use the default dispatch. + return default_dispatch; +} + + +void +GTM::gtm_thread::set_default_dispatch(GTM::abi_dispatch* disp) +{ + if (default_dispatch == disp) + return; + if (default_dispatch) + { + // If we are switching method groups, initialize and shut down properly. + if (default_dispatch->get_method_group() != disp->get_method_group()) + { + default_dispatch->get_method_group()->fini(); + disp->get_method_group()->init(); + } + } + else + disp->get_method_group()->init(); + default_dispatch = disp; +} + + +static GTM::abi_dispatch* +parse_default_method() +{ + const char *env = getenv("ITM_DEFAULT_METHOD"); + GTM::abi_dispatch* disp = 0; + if (env == NULL) + return 0; + + while (isspace((unsigned char) *env)) + ++env; + if (strncmp(env, "serialirr_onwrite", 17) == 0) + { + disp = GTM::dispatch_serialirr_onwrite(); + env += 17; + } + else if (strncmp(env, "serialirr", 9) == 0) + { + disp = GTM::dispatch_serialirr(); + env += 9; + } + else if (strncmp(env, "serial", 6) == 0) + { + disp = GTM::dispatch_serial(); + env += 6; + } + else if (strncmp(env, "gl_wt", 5) == 0) + { + disp = GTM::dispatch_gl_wt(); + env += 5; + } + else + goto unknown; + + while (isspace((unsigned char) *env)) + ++env; + if (*env == '\0') + return disp; + + unknown: + GTM::GTM_error("Unknown TM method in environment variable " + "ITM_DEFAULT_METHOD\n"); + return 0; +} + +// Gets notifications when the number of registered threads changes. This is +// used to initialize the method set choice and trigger straightforward choice +// adaption. +// This must be called only by serial threads. +void +GTM::gtm_thread::number_of_threads_changed(unsigned previous, unsigned now) +{ + if (previous == 0) + { + // No registered threads before, so initialize. + static bool initialized = false; + if (!initialized) + { + initialized = true; + // Check for user preferences here. + default_dispatch_user = parse_default_method(); + } + } + else if (now == 0) + { + // No registered threads anymore. The dispatch based on serial mode do + // not have any global state, so this effectively shuts down properly. + set_default_dispatch(dispatch_serialirr()); + } + + if (now == 1) + { + // Only one thread, so use a serializing method. + // ??? If we don't have a fast serial mode implementation, it might be + // better to use the global lock method set here. + if (default_dispatch_user) + set_default_dispatch(default_dispatch_user); + else + set_default_dispatch(dispatch_serialirr()); + } + else if (now > 1 && previous <= 1) + { + // More than one thread, use the default method. + if (default_dispatch_user) + set_default_dispatch(default_dispatch_user); + else + set_default_dispatch(dispatch_serialirr_onwrite()); + } +} |