From: Peter Zijlstra <peterz@infradead.org>
To: Josh Triplett <josh@joshtriplett.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com,
edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com,
oleg@redhat.com, bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 6/7] rcu: Make expedited grace periods recheck dyntick idle state
Date: Mon, 14 Nov 2016 18:37:33 +0100 [thread overview]
Message-ID: <20161114173733.GJ3142@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20161114172512.bcwdy66elesds5t4@jtriplet-mobl2.jf.intel.com>
On Mon, Nov 14, 2016 at 09:25:12AM -0800, Josh Triplett wrote:
> On Mon, Nov 14, 2016 at 08:57:12AM -0800, Paul E. McKenney wrote:
> > Expedited grace periods check dyntick-idle state, and avoid sending
> > IPIs to idle CPUs, including those running guest OSes, and, on NOHZ_FULL
> > kernels, nohz_full CPUs. However, the kernel has been observed checking
> > a CPU while it was non-idle, but sending the IPI after it has gone
> > idle. This commit therefore rechecks idle state immediately before
> > sending the IPI, refraining from IPIing CPUs that have since gone idle.
> >
> > Reported-by: Rik van Riel <riel@redhat.com>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> atomic_add_return(0, ...) seems odd. Do you actually want that, rather
> than atomic_read(...)? If so, can you please document exactly why?
Yes that is weird. The only effective difference is that it would do a
load-exclusive instead of a regular load.
next prev parent reply other threads:[~2016-11-14 17:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-14 16:56 [PATCH tip/core/rcu 0/7] Miscellaneous fixes for 4.10 Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 1/7] rcu: Tighten up __call_rcu() rcu_head alignment check Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 2/7] rcu: Remove obsolete rcu_check_callbacks() header comment Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 3/7] rcu: Remove obsolete comment from __call_rcu() Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 4/7] rcu: RCU_TRACE enables event tracing as well as debugfs Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 5/7] torture: Trace long read-side delays Paul E. McKenney
2016-11-14 17:21 ` Josh Triplett
2016-11-14 18:44 ` Paul E. McKenney
2016-11-14 18:54 ` Josh Triplett
2016-11-14 16:57 ` [PATCH tip/core/rcu 6/7] rcu: Make expedited grace periods recheck dyntick idle state Paul E. McKenney
2016-11-14 17:25 ` Josh Triplett
2016-11-14 17:37 ` Peter Zijlstra [this message]
2016-11-14 18:12 ` Paul E. McKenney
2016-11-15 8:16 ` Peter Zijlstra
2016-11-15 14:36 ` Paul E. McKenney
2016-11-14 16:57 ` [PATCH tip/core/rcu 7/7] rcu: Don't kick unless grace period or request Paul E. McKenney
2016-11-14 17:26 ` [PATCH tip/core/rcu 0/7] Miscellaneous fixes for 4.10 Josh Triplett
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