On 03/30/2015 12:20 PM, Chris Metcalf wrote:
> I wanted to ping the patch below again, since I haven't heard any
> feedback.
>
> I note that Rik van Riel's change posted this weekend offers similar
> functionality for userspace. My change offers a convenient API
> for, e.g., kernel drivers setting up default irq balancing.
>
> https://lkml.org/lkml/2015/3/28/94
I submitted a patch to irqbalance to exclude nohz_full
cpus from having irqs assigned to them. I could see
the same thing being useful for in-kernel irq assignment,
especially for multi-queue devices that set up irqs on
multiple CPUs.
> An alternate API would be one that just returned the full no_hz
> cpumask to kernel callers; I'd be happy with that as well, but my
> instinct was to make the API as narrow as possible to start with.
>
> Comments?
What drivers and subsystems are you targeting?
I am just looking at blk-mq now, and it seems like the
API most appropriate for that would be an inline function
that tests whether or not a CPU is nohz_full.
for_each_possible_cpu(i) {
...
if (cpu_nohz_full(i))
continue;
}
A lot of the other code in drivers and subsystems that
set up per-cpu queues and irqs seem to iterate over all
CPUs at init time, and could benefit from a function
allowing them to skip nohz_full CPUs.
Your tick_nohz_full_clear_cpus() function seems reasonable
too, for code that uses a cpumask to set up per cpu stuff.
> On 03/24/2015 03:21 PM, cmetc...@ezchip.com wrote:
>> From: Chris Metcalf <cmetc...@ezchip.com>
>>
>> This is useful, for example, to modify a cpumask to avoid the
>> nohz cores so that interrupts aren't sent to them.
>>
>> Signed-off-by: Chris Metcalf <cmetc...@ezchip.com>
>> ---
>> Motivated by patch 4/4 in this series.
>>
>> include/linux/tick.h | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/include/linux/tick.h b/include/linux/tick.h
>> index 9c085dc12ae9..d53ad4892a39 100644
>> --- a/include/linux/tick.h
>> +++ b/include/linux/tick.h
>> @@ -186,6 +186,12 @@ static inline bool tick_nohz_full_cpu(int cpu)
>> return cpumask_test_cpu(cpu, tick_nohz_full_mask);
>> }
>> +static inline void tick_nohz_full_clear_cpus(struct cpumask *mask)
>> +{
>> + if (tick_nohz_full_enabled())
>> + cpumask_andnot(mask, mask, tick_nohz_full_mask);
>> +}
>> +
>> extern void __tick_nohz_full_check(void);
>> extern void tick_nohz_full_kick(void);
>> extern void tick_nohz_full_kick_cpu(int cpu);
>> @@ -194,6 +200,7 @@ extern void __tick_nohz_task_switch(struct
>> task_struct *tsk);
>> #else
>> static inline bool tick_nohz_full_enabled(void) { return false; }
>> static inline bool tick_nohz_full_cpu(int cpu) { return false; }
>> +static inline void tick_nohz_full_clear_cpus(struct cpumask *mask) { }
>> static inline void __tick_nohz_full_check(void) { }
>> static inline void tick_nohz_full_kick_cpu(int cpu) { }
>> static inline void tick_nohz_full_kick(void) { }
>
--
All rights reversed
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
