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From: Frederic Weisbecker <frederic@kernel.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>, rcu@vger.kernel.org
Subject: Re: need_heavy_qs flag for PREEMPT=y kernels
Date: Mon, 19 Aug 2019 14:34:32 +0200
Message-ID: <20190819123432.GB27088@lenoir> (raw)
In-Reply-To: <20190816000201.GC225926@google.com>

On Thu, Aug 15, 2019 at 08:02:01PM -0400, Joel Fernandes wrote:
> On Thu, Aug 15, 2019 at 02:45:42PM -0700, Paul E. McKenney wrote:
> > As I understand it, tick_dep_mask forces the tick on globally,
> > ts->tick_dep_mask forces it on for a specific CPU (which RCU uses when it
> > needs a quiescent state from that CPU), current->tick_dep_mask forces
> > it on for a specific task (which RCU uses for callback invocation
> > and certain rcutorture kthreads), and I don't pretend to understand
> > current->signal->tick_dep_mask (the comment says something about POSIX
> > CPU timers).
> 
> Right. I am pretty new to all of these so I could have something incorrect in
> a hurry. But thanks for the explanation of your understanding of these.
> 
> Yes this commit talks about timers as well for the signal->tick_dep_mask:
> d027d45d8a17 ("nohz: New tick dependency mask")

FWIW, the signal->tick_dep_mask is a thread group wide tick dependency. I'm
not proud of that requirement but we need to keep it for posix CPU timers
that can elapse a timer on all threads of a same process and the tick is
the cheapest way to account for that.


  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-11 18:08 Joel Fernandes
2019-08-11 18:34 ` Joel Fernandes
2019-08-11 21:16   ` Paul E. McKenney
2019-08-11 21:25     ` Joel Fernandes
2019-08-11 23:30       ` Paul E. McKenney
2019-08-12  1:24         ` Joel Fernandes
2019-08-12  1:40           ` Joel Fernandes
2019-08-12  3:57             ` Paul E. McKenney
2019-08-11 21:13 ` Paul E. McKenney
2019-08-12  3:21   ` Joel Fernandes
2019-08-12  3:53     ` Paul E. McKenney
2019-08-12 21:20       ` Joel Fernandes
2019-08-12 23:01         ` Paul E. McKenney
2019-08-13  1:02           ` Joel Fernandes
2019-08-13  1:05             ` Joel Fernandes
2019-08-13  2:28               ` Paul E. McKenney
2019-08-13  2:27             ` Paul E. McKenney
2019-08-13  2:50               ` Paul E. McKenney
2019-08-15 17:17             ` Paul E. McKenney
2019-08-15 20:04               ` Joel Fernandes
2019-08-15 20:31                 ` Paul E. McKenney
2019-08-15 21:22                   ` Joel Fernandes
2019-08-15 21:27                     ` Joel Fernandes
2019-08-15 21:34                       ` Joel Fernandes
2019-08-15 21:57                         ` Paul E. McKenney
2019-08-15 21:45                     ` Paul E. McKenney
2019-08-16  0:02                       ` Joel Fernandes
2019-08-19 12:34                         ` Frederic Weisbecker [this message]
2019-08-19 12:09                   ` Frederic Weisbecker
2019-08-19 16:57                   ` Frederic Weisbecker
2019-08-19 22:31                     ` Paul E. McKenney

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