Re: [PATCH V6 04/16] rv/include: Add deterministic automata monitor definition via C macros

[Daniel Bristot de Oliveira <bristot@kernel.org>]

On 7/20/22 22:06, Steven Rostedt wrote:
>> +/*												\
>> + * da_monitor_enabled_##name - checks if the monitor is enabled					\
>> + */												\
>> +static inline bool da_monitor_enabled_##name(void)						\
>> +{												\
> Should we add a:
> 
> 	smp_rmb();
> 
> here? And then a smp_wmb() where these switches get updated?
>

Makes sense.

Should I also add the READ_ONCE/WRITE_ONCE? like

smp_rmb()
READ_ONCE(var)

WRITE_ONCE(var, value)
smp_wmb()

for all these on/off knobs, or just the barriers?

> I guess how critical is it that these turn off immediately after the switch
> is flipped?

It is not critical to continue the execution of those that have already crossed by
the variable. Still, waiting for the tracepoints to finish their execution before
returning to the user-space task that disabled the variable might be a good thing.

IIRC, we can do that via RCU... like, synchronize_rcu()?

>> +	/* global switch */									\
>> +	if (unlikely(!rv_monitoring_on()))							\
>> +		return 0;									\
>> +												\
>> +	/* monitor enabled */									\
>> +	if (unlikely(!rv_##name.enabled))							\
>> +		return 0;									\
>> +												\
>> +	return 1;										\
>> +}												\
>> +												\