linux-kernel - Re: [PATCH RFC 1/8] perf/core: Add *group_leader to perf_event_create_kernel

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Date:   Wed, 14 Dec 2022 09:22:29 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Marc Zyngier <maz@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>, kvmarm@...ts.linux.dev,
        linux-perf-users@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH RFC 1/8] perf/core: Add *group_leader to
 perf_event_create_kernel_counter()

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 7f04f995c975..f671b1a9a691 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -12674,12 +12674,14 @@ SYSCALL_DEFINE5(perf_event_open,
>   * @attr: attributes of the counter to create
>   * @cpu: cpu in which the counter is bound
>   * @task: task to profile (NULL for percpu)
> + * @group_leader: event group leader
>   * @overflow_handler: callback to trigger when we hit the event
>   * @context: context data could be used in overflow_handler callback
>   */
>  struct perf_event *
>  perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
>  				 struct task_struct *task,
> +				 struct perf_event *group_leader,
>  				 perf_overflow_handler_t overflow_handler,
>  				 void *context)
>  {
> @@ -12694,7 +12696,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
>  	if (attr->aux_output)
>  		return ERR_PTR(-EINVAL);
>  
> -	event = perf_event_alloc(attr, cpu, task, NULL, NULL,
> +	event = perf_event_alloc(attr, cpu, task, group_leader, NULL,
>  				 overflow_handler, context, -1);

Grouping involves lot of complexities. Setting group_leader won't be sufficient.
Please see perf_event_open() syscall code for more detail.

Thanks,
Ravi