lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 13 Aug 2014 15:56:23 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Pranith Kumar <bobby.prani@...il.com> Cc: Josh Triplett <josh@...htriplett.org>, Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Lai Jiangshan <laijs@...fujitsu.com>, "open list:READ-COPY UPDATE..." <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads On Tue, Aug 12, 2014 at 01:07:47PM -0400, Pranith Kumar wrote: > Updated changelog regarding the removed comment about the implied barrier > provided by wake_up() logic. > > -- > Pranith Queued for 3.18, thank you! Thanx, Paul > The rcu_gp_kthread_wake() function checks for three conditions before waking up > grace period kthreads: > > * Is the thread we are trying to wake up the current thread? > * Are the gp_flags zero? (all threads wait on non-zero gp_flags condition) > * Is there no thread created for this flavour, hence nothing to wake up? > > If any one of these condition is true, we do not call wake_up(). > It was found that there are quite a few avoidable wake ups both during > idle time and under stress induced by rcutorture. > > Idle: > > Total:66000, unnecessary:66000, case1:61827, case2:66000, case3:0 > Total:68000, unnecessary:68000, case1:63696, case2:68000, case3:0 > > rcutorture: > > Total:254000, unnecessary:254000, case1:199913, case2:254000, case3:0 > Total:256000, unnecessary:256000, case1:201784, case2:256000, case3:0 > > Here case{1-3} are the cases listed above. We can avoid these wake ups by using > rcu_gp_kthread_wake() to conditionally wake up the grace period kthreads. > > There is a comment about an implied barrier supplied by the wake_up() logic. > This barrier is necessary for the awakened thread to see the updated ->gp_flags. > This flag is always being updated with the root node lock held. Also, the > awakened thread tries to acquire the root node lock before reading ->gp_flags > because of which there is proper ordering. > > Hence this commit tries to avoid calling wake_up() whenever we can by using > rcu_gp_kthread_wake() function. > > Signed-off-by: Pranith Kumar <bobby.prani@...il.com> > CC: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> > --- > kernel/rcu/tree.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index b63517c..6b68d2d 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1938,7 +1938,7 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) > { > WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); > raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); > - wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ > + rcu_gp_kthread_wake(rsp); > } > > /* > @@ -2516,7 +2516,7 @@ static void force_quiescent_state(struct rcu_state *rsp) > ACCESS_ONCE(rsp->gp_flags) = > ACCESS_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS; > raw_spin_unlock_irqrestore(&rnp_old->lock, flags); > - wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ > + rcu_gp_kthread_wake(rsp); > } > > /* > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists