linux-kernel - Re: [PATCH 2/7] perf: Add PERF_EV_CAP_READ

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Message-ID: <ff22bcc8-98a2-4975-91e8-29740e6dac45@linux.intel.com>
Date: Fri, 6 Sep 2024 11:26:36 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
 irogers@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] perf: Add PERF_EV_CAP_READ_SCOPE



On 2024-09-06 11:11 a.m., Peter Zijlstra wrote:
> On Fri, Aug 02, 2024 at 08:16:38AM -0700, kan.liang@...ux.intel.com wrote:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> Usually, an event can be read from any CPU of the scope. It doesn't need
>> to be read from the advertised CPU.
>>
>> Add a new event cap, PERF_EV_CAP_READ_SCOPE. An event of a PMU with
>> scope can be read from any active CPU in the scope.
>>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>  include/linux/perf_event.h |  3 +++
>>  kernel/events/core.c       | 14 +++++++++++---
>>  2 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 1102d5c2be70..1206bc86eb4f 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -633,10 +633,13 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
>>   * PERF_EV_CAP_SIBLING: An event with this flag must be a group sibling and
>>   * cannot be a group leader. If an event with this flag is detached from the
>>   * group it is scheduled out and moved into an unrecoverable ERROR state.
>> + * PERF_EV_CAP_READ_SCOPE: A CPU event that can be read from any CPU of the
>> + * PMU scope where it is active.
>>   */
>>  #define PERF_EV_CAP_SOFTWARE		BIT(0)
>>  #define PERF_EV_CAP_READ_ACTIVE_PKG	BIT(1)
>>  #define PERF_EV_CAP_SIBLING		BIT(2)
>> +#define PERF_EV_CAP_READ_SCOPE		BIT(3)
>>  
>>  #define SWEVENT_HLIST_BITS		8
>>  #define SWEVENT_HLIST_SIZE		(1 << SWEVENT_HLIST_BITS)
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 5e1877c4cb4c..c55294f34575 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -4463,16 +4463,24 @@ struct perf_read_data {
>>  	int ret;
>>  };
>>  
>> +static inline const struct cpumask *perf_scope_cpu_topology_cpumask(unsigned int scope, int cpu);
>> +
>>  static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
>>  {
>> +	int local_cpu = smp_processor_id();
>>  	u16 local_pkg, event_pkg;
>>  
>>  	if ((unsigned)event_cpu >= nr_cpu_ids)
>>  		return event_cpu;
>>  
>> -	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
>> -		int local_cpu = smp_processor_id();
>> +	if (event->group_caps & PERF_EV_CAP_READ_SCOPE) {
>> +		const struct cpumask *cpumask = perf_scope_cpu_topology_cpumask(event->pmu->scope, event_cpu);
>> +
>> +		if (cpumask && cpumask_test_cpu(local_cpu, cpumask))
>> +			return local_cpu;
>> +	}
>>  
>> +	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
> 
> I'm guessing the goal is to eventually remove this one, right?

Yes, after I have the uncore cleaned up. It should be able to remove the
PERF_EV_CAP_READ_ACTIVE_PKG.

Thanks,
Kan
>