Re: [PATCH RFC tip/core/rcu] SRCU rewrite

[Mathieu Desnoyers]

----- On Nov 15, 2016, at 2:51 AM, Peter Zijlstra peterz@xxxxxxxxxxxxx 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