• Frederic Weisbecker's avatar
    nohz: Separate out irq exit and idle loop dyntick logic · 280f0677
    Frederic Weisbecker authored
    The tick_nohz_stop_sched_tick() function, which tries to delay
    the next timer tick as long as possible, can be called from two
    places:
    
    - From the idle loop to start the dytick idle mode
    - From interrupt exit if we have interrupted the dyntick
    idle mode, so that we reprogram the next tick event in
    case the irq changed some internal state that requires this
    action.
    
    There are only few minor differences between both that
    are handled by that function, driven by the ts->inidle
    cpu variable and the inidle parameter. The whole guarantees
    that we only update the dyntick mode on irq exit if we actually
    interrupted the dyntick idle mode, and that we enter in RCU extended
    quiescent state from idle loop entry only.
    
    Split this function into:
    
    - tick_nohz_idle_enter(), which sets ts->inidle to 1, enters
    dynticks idle mode unconditionally if it can, and enters into RCU
    extended quiescent state.
    
    - tick_nohz_irq_exit() which only updates the dynticks idle mode
    when ts->inidle is set (ie: if tick_nohz_idle_enter() has been called).
    
    To maintain symmetry, tick_nohz_restart_sched_tick() has been renamed
    into tick_nohz_idle_exit().
    
    This simplifies the code and micro-optimize the irq exit path (no need
    for local_irq_save there). This also prepares for the split between
    dynticks and rcu extended quiescent state logics. We'll need this split to
    further fix illegal uses of RCU in extended quiescent states in the idle
    loop.
    Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Cc: Mike Frysinger <vapier@gentoo.org>
    Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
    Cc: David Miller <davem@davemloft.net>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Russell King <linux@arm.linux.org.uk>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Paul Mundt <lethal@linux-sh.org>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
    280f0677
softirq.c 22.1 KB