linux-kernel - [RFC 0/5] rcu: Introduce leaf_node_for_each_mask_possible

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Date:   Fri,  9 Dec 2016 16:48:22 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [RFC 0/5] rcu: Introduce leaf_node_for_each_mask_possible_cpu() and its friend

Hi Paul,

While reading the discussion at:

https://marc.info/?l=linux-kernel&m=148044253400769

I figured we might use this fact to save some extra checks in RCU core code,
currently we iterate over all the possible CPUs on a leaf node, check whether
they were masked in a certain mask and do something. However, given the fact
that the masks on a leaf node should always be sparse than the corresponding
part of cpu_possible_mask, we'd better iterate over all bits in a mask and
check whether the corresponding CPU is possible or not.

So I made this RFC, I did a simple build/boot/rcutorture test on my box with
SMP=4, nothing bad happens. Currently I'm waiting for the 0day and trying to
test this one a bigger system, in the meanwhile, looking forwards to any
comment and suggestion.

So thoughts?

Regards,
Boqun