Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging normal ones

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Jul 2, 2015, at 2:35 PM, Ingo Molnar mingo@kernel.org wrote:

> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> 
>> > And it's not like it's that hard to stem the flow of algorithmic sloppiness at
>> > the source, right?
>> 
>> OK, first let me make sure that I understand what you are asking for:
>> 
>> 1.	Completely eliminate synchronize_rcu_expedited() and
>> 	synchronize_sched_expedited(), replacing all uses with their
>> 	unexpedited counterparts.  (Note that synchronize_srcu_expedited()
>> 	does not wake up CPUs, courtesy of its read-side memory barriers.)
>> 	The fast-boot guys are probably going to complain, along with
>> 	the networking guys.
>> 
>> 2.	Keep synchronize_rcu_expedited() and synchronize_sched_expedited(),
>> 	but push back hard on any new uses and question any existing uses.
>> 
>> 3.	Revert 74b51ee152b6 ("ACPI / osl: speedup grace period in
>> 	acpi_os_map_cleanup").
>> 
>> 4.	Something else?
> 
> I'd love to have 1) but 2) would be a realistic second best option? ;-)

Perhaps triggering a printk warning if use of
synchronize_{rcu,sched}_expedited() go beyond of certain rate might be
another option ? If we detect that a caller calls it too often, we could
emit a printk warning with a stack trace. This should ensure everyone
is very careful about where they use it.

Thanks,

Mathieu

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