On Thu, Aug 30, 2012 at 02:05:18PM -0700, Paul E. McKenney wrote: > From: Frederic Weisbecker <[email protected]> > > RCU currently insists that only idle tasks can enter RCU idle mode, which > prohibits an adaptive tickless kernel (AKA nohz cpusets), which in turn > would mean that usermode execution would always take scheduling-clock > interrupts, even when there is only one task runnable on the CPU in > question. > > This commit therefore adds rcu_user_enter() and rcu_user_exit(), which > allow non-idle tasks to enter RCU idle mode. These are quite similar > to rcu_idle_enter() and rcu_idle_exit(), respectively, except that they > omit the idle-task checks. > > [ Updated to use "user" flag rather than separate check functions. ] > > Signed-off-by: Frederic Weisbecker <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Cc: Alessio Igor Bogani <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Avi Kivity <[email protected]> > Cc: Chris Metcalf <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Daniel Lezcano <[email protected]> > Cc: Geoff Levand <[email protected]> > Cc: Gilad Ben Yossef <[email protected]> > Cc: Hakan Akkan <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Kevin Hilman <[email protected]> > Cc: Max Krasnyansky <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Stephen Hemminger <[email protected]> > Cc: Steven Rostedt <[email protected]> > Cc: Sven-Thorsten Dietrich <[email protected]> > Cc: Thomas Gleixner <[email protected]>
A few suggestions below: an optional microoptimization and some bugfixes. With the bugfixes, and with or without the microoptimization: Reviewed-by: Josh Triplett <[email protected]> > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c [...] > -static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long > oldval) > +static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval, > + bool user) > { > trace_rcu_dyntick("Start", oldval, 0); > - if (!is_idle_task(current)) { > + if (!is_idle_task(current) && !user) { Microoptimization: putting the !user check first (here and in the exit function) would allow the compiler to partially inline rcu_eqs_*_common into the two trivial wrappers and constant-fold away the test for !user. > +void rcu_idle_enter(void) > +{ > + rcu_eqs_enter(0); > +} s/0/false/ > +void rcu_user_enter(void) > +{ > + rcu_eqs_enter(1); > +} s/1/true/ > -static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) > +static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval, > + int user) > { > smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */ > atomic_inc(&rdtp->dynticks); > @@ -464,7 +490,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks > *rdtp, long long oldval) > WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); > rcu_cleanup_after_idle(smp_processor_id()); > trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting); > - if (!is_idle_task(current)) { > + if (!is_idle_task(current) && !user) { Same micro-optimization as the enter function. > +void rcu_idle_exit(void) > +{ > + rcu_eqs_exit(0); > +} s/0/false/ > +void rcu_user_exit(void) > +{ > + rcu_eqs_exit(1); > +} s/1/true/ > @@ -539,7 +586,7 @@ void rcu_irq_enter(void) > if (oldval) > trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting); > else > - rcu_idle_exit_common(rdtp, oldval); > + rcu_eqs_exit_common(rdtp, oldval, 1); s/1/true/, and likewise in rcu_irq_exit. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
