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McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, linux-mm@kvack.org Subject: Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls Message-ID: <20200623210111.GA117936@google.com> References: <20200623002128.GA25456@paulmck-ThinkPad-P72> <20200623002147.25750-2-paulmck@kernel.org> <20200623193431.GA68372@google.com> <20200623205508.GS9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623205508.GS9247@paulmck-ThinkPad-P72> X-Rspamd-Queue-Id: 62CB8180F8B90 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000933, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 23, 2020 at 01:55:08PM -0700, Paul E. McKenney wrote: [..] > > Just for my understanding, cond_resched_tasks_rcu_qs() may not help here > > because preemption is not disabled right? Still I see no harm in using it > > here either as it may give a slight speed up for tasks-RCU. > > The RCU-tasks stall-warning interval is ten minutes, and I have not yet > seen evidence that we are getting close to that. If we do, then yes, > a cond_resched_tasks_rcu_qs() might be in this code's future. But it > does add overhead, so we need to see the evidence first. Yes, true about that overhead. Ok, this is fine with me too, thanks :) - Joel