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Date:   Fri, 18 May 2018 11:36:23 -0700
From:   Joel Fernandes <joel@joelfernandes.org>
To:     paulmck@linux.vnet.ibm.com, rostedt@goodmis.org,
        byungchul.park@lge.com, mathieu.desnoyers@efficios.com,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     kernel-team@android.com
Subject: Tasks RCU vs Preempt RCU
Message-ID: <20180518183623.GA163151@joelaf.mtv.corp.google.com>
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Hi,

I was thinking about tasks-RCU and why its needed. Since preempt-RCU allows
tasks to be preempted in read-sections, can we not just reuse that mechanism
for the trampolines since we track all preempted tasks so we would wait on
all tasks preempted within a trampoline?

I am trying to understand what will _not_ work if we did that.. I'm guessing
the answer is that that would mean the trampoline has to be wrapped with
rcu_read_{lock,unlock} which may add some overhead, but please let me know
if I'm missing something else..

The advantage I guess is possible elimination of an RCU variant, and also
possibly eliminating the tasks RCU thread that monitors.. Anyway I was
thinking more in terms of the effort of reduction of the RCU flavors etc and
reducing complexity ideas.

thanks!

- Joel