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Date: Tue, 15 Nov 2016 13:54:50 +0000 (UTC)
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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Subject: Re: [PATCH RFC tip/core/rcu] SRCU rewrite
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----- On Nov 15, 2016, at 2:51 AM, Peter Zijlstra peterz@infradead.org wrote:

> On Mon, Nov 14, 2016 at 10:36:36AM -0800, Paul E. McKenney wrote:
>> SRCU uses two per-cpu counters: a nesting counter to count the number of
>> active critical sections, and a sequence counter to ensure that the nesting
>> counters don't change while they are being added together in
>> srcu_readers_active_idx_check().
>> 
>> This patch instead uses per-cpu lock and unlock counters. Because the both
>> counters only increase and srcu_readers_active_idx_check() reads the unlock
>> counter before the lock counter, this achieves the same end without having
>> to increment two different counters in srcu_read_lock(). This also saves a
>> smp_mb() in srcu_readers_active_idx_check().
> 
> A very small improvement... I feel SRCU has much bigger issues :/

Do you have specific issues in mind ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com