----- Original Message ----- > From: "Mathieu Desnoyers" <mathieu.desnoy...@efficios.com> > To: paul...@linux.vnet.ibm.com > Cc: fweis...@gmail.com, pet...@infradead.org, linux-kernel@vger.kernel.org > Sent: Sunday, March 30, 2014 11:29:25 PM > Subject: Re: Promela/spin model for NO_HZ_FULL_SYSIDLE code > > ----- Original Message ----- > > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> > > To: fweis...@gmail.com, "mathieu desnoyers" > > <mathieu.desnoy...@efficios.com>, pet...@infradead.org > > Cc: linux-kernel@vger.kernel.org > > Sent: Sunday, March 30, 2014 7:08:56 PM > > Subject: Promela/spin model for NO_HZ_FULL_SYSIDLE code > > > > For whatever it is worth, the following model claims safety and progress > > for the sysidle state machine. > > > > Thoughts? > > Hi Paul, > > Please keep in mind that it's been a while since I've looked at Promela > proofs, but a couple of questions come to mind. First, how is the execution > script below checking for progress in any way ? I remember that we used > the negation of a "_np" LTL claim to check for progress in the past. > Moreover, I'd be much more comfortable seeing ifdefs in the code that inject > known failures, and let them be triggered by error-triggering runs in the > scripts (with e.g. -DINJECT_ERROR_XYZ), to confirm that this model actually > catches known issues. > > If we can show that the model can detect a few failure modes, both for safety > and progress, then my confidence level in the model will start to improve. > ;-)
Digging through the spin documentation, "-l" is indeed another way besides the _np LTL negation to find non-progress cycles. Still, injecting known failures would let us learn a lot about the model error detection abilities. Thanks! Mathieu > > Thanks, > > Mathieu > > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > sysidle.sh > > ------------------------------------------------------------------------ > > spin -a sysidle.spin > > cc -DNP -o pan pan.c > > # Fair scheduling to focus progress checks in timekeeper. > > ./pan -f -l -m1280000 -w22 > > > > ------------------------------------------------------------------------ > > sysidle.spin > > ------------------------------------------------------------------------ > > /* > > * Promela model for CONFIG_NO_HZ_FULL_SYSIDLE=y in the Linux kernel. > > * This model assumes that the dyntick-idle bit manipulation works based > > * on long usage, and substitutes a per-thread boolean "am_busy[]" array > > * for the Linux kernel's dyntick-idle masks. The focus of this model > > * is therefore on the state machine itself. Checks for both safety and > > * forward progress. > > * > > * This program 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 2 of the License, or > > * (at your option) any later version. > > * > > * This program 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. > > * > > * You should have received a copy of the GNU General Public License > > * along with this program; if not, you can access it online at > > * http://www.gnu.org/licenses/gpl-2.0.html. > > * > > * Copyright IBM Corporation, 2014 > > * > > * Author: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > */ > > > > #define NUM_WORKERS 3 > > > > byte wakeup_timekeeper = 0; /* Models rcu_kick_nohz_cpu(). */ > > > > #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ > > #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ > > #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ > > #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ > > #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle > > state. */ > > > > byte full_sysidle_state = RCU_SYSIDLE_NOT; > > > > byte am_busy[NUM_WORKERS]; /* Busy is similar to "not dyntick-idle". */ > > byte am_setup[NUM_WORKERS]; /* Setup means timekeeper knows I am not idle. > > */ > > > > /* > > * Non-timekeeping CPU going into and out of dyntick-idle state. > > */ > > proctype worker(byte me) > > { > > byte oldstate; > > > > do > > :: 1 -> > > /* Go idle. */ > > am_setup[me] = 0; > > am_busy[me] = 0; > > > > /* Dyntick-idle in the following loop. */ > > do > > :: 1 -> skip; > > :: 1 -> break; > > od; > > > > /* Exit idle loop, model getting out of dyntick idle state. */ > > am_busy[me] = 1; > > > > /* Get state out of full-system idle states. */ > > atomic { > > oldstate = full_sysidle_state; > > if > > :: oldstate > RCU_SYSIDLE_SHORT -> > > full_sysidle_state = RCU_SYSIDLE_NOT; > > :: else -> skip; > > fi; > > } > > > > /* If needed, wake up the timekeeper. */ > > if > > :: oldstate == RCU_SYSIDLE_FULL_NOTED -> > > wakeup_timekeeper = 1; > > :: else -> skip; > > fi; > > > > /* Mark ourselves fully awake and operational. */ > > am_setup[me] = 1; > > > > /* We are fully awake, so timekeeper must not be asleep. */ > > assert(full_sysidle_state < RCU_SYSIDLE_FULL); > > > > /* Running in kernel in the following loop. */ > > do > > :: 1 -> skip; > > :: 1 -> break; > > od; > > od > > } > > > > /* > > * Are all the workers in dyntick-idle state? > > */ > > #define check_idle() \ > > i = 0; \ > > idle = 1; \ > > do \ > > :: i < NUM_WORKERS -> \ > > if \ > > :: am_busy[i] == 1 -> idle = 0; \ > > :: else -> skip; \ > > fi; \ > > i++; \ > > :: i >= NUM_WORKERS -> break; \ > > od > > > > /* > > * Timekeeping CPU. > > */ > > proctype timekeeper() > > { > > byte i; > > byte idle; > > byte curstate; > > byte newstate; > > > > do > > :: 1 -> > > /* Capture current state. */ > > check_idle(); > > curstate = full_sysidle_state; > > newstate = curstate; > > > > /* Check for acceptance state. */ > > if > > :: idle == 0 -> > > progress_idle: > > skip; > > :: curstate == RCU_SYSIDLE_NOT -> > > progress_idle_reset: > > skip; > > :: else -> skip; > > fi; > > > > /* Manage state... */ > > if > > :: idle == 1 && curstate < RCU_SYSIDLE_FULL_NOTED -> > > /* Idle, advance to next state. */ > > atomic { > > if > > :: full_sysidle_state == curstate -> > > newstate = curstate + 1; > > full_sysidle_state = newstate; > > :: else -> skip; > > fi; > > } > > :: idle == 0 && full_sysidle_state >= RCU_SYSIDLE_LONG -> > > /* Non-idle and state advanced, revert to base state. */ > > full_sysidle_state = RCU_SYSIDLE_NOT; > > :: else -> skip; > > fi; > > > > /* If in RCU_SYSIDLE_FULL_NOTED, wait to be awakened. */ > > do > > :: newstate != RCU_SYSIDLE_FULL_NOTED && > > wakeup_timekeeper == 1 -> > > assert(0); /* Should never get here. */ > > :: newstate != RCU_SYSIDLE_FULL_NOTED && > > wakeup_timekeeper == 0 -> > > break; > > :: newstate == RCU_SYSIDLE_FULL_NOTED && > > wakeup_timekeeper == 1 -> > > progress_full_system_idle_1: > > assert(full_sysidle_state == RCU_SYSIDLE_NOT); > > wakeup_timekeeper = 0; > > break; > > :: newstate == RCU_SYSIDLE_FULL_NOTED && > > wakeup_timekeeper == 0 -> > > progress_full_system_idle_2: > > > > /* We are asleep, so all workers better be idle. */ > > atomic { > > i = 0; > > idle = 1; > > do > > :: i < NUM_WORKERS -> > > if > > :: am_setup[i] -> idle = 0; > > :: else -> skip; > > fi; > > i++; > > :: i >= NUM_WORKERS -> break; > > od; > > assert(idle == 1 || > > full_sysidle_state < RCU_SYSIDLE_FULL); > > } > > od; > > assert(full_sysidle_state <= RCU_SYSIDLE_FULL_NOTED); > > od; > > } > > > > init { > > byte i = 0; > > > > do > > :: i < NUM_WORKERS -> > > am_busy[i] = 1; > > am_setup[i] = 1; > > run worker(i); > > i++; > > :: i >= NUM_WORKERS -> break; > > od; > > run timekeeper(); > > } > > > > > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
