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Date:   Mon, 2 Dec 2019 12:25:35 -0800
From:   Andi Kleen <ak@linux.intel.com>
To:     "Liang, Kan" <kan.liang@linux.intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, mingo@redhat.com,
        acme@kernel.org, tglx@linutronix.de, bp@alien8.de,
        linux-kernel@vger.kernel.org, eranian@google.com,
        alexey.budankov@linux.intel.com, vitaly.slobodskoy@intel.com
Subject: Re: [RFC PATCH 3/8] perf: Init/fini PMU specific data
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Looks reasonable to me.

> //get current number of threads
> read_lock(&tasklist_lock);
> for_each_process_thread(g, p)
> 	num_thread++;
> read_unlock(&tasklist_lock);

I'm sure we have that count somewhere.

> 
> //allocate the space for them
> for (i = 0; i < num_thread; i++)
> 	data[i] = kzalloc(ctx_size, flags);
> i = 0;
> 
> /*
>  * Assign the space to tasks
>  * There may be some new threads created when we allocate space.
>  * new_task will track its number.
>  */
> raw_spin_lock_irqsave(&task_data_events_lock, flags);
> 
> if (atomic_inc_return(&nr_task_data_events) > 1)
> 	goto unlock;
> 
> for_each_process_thread(g, p) {
> 	if (i < num_thread)
> 		p->perf_ctx_data = data[i++];
> 	else
> 		new_task++;
> }
> raw_spin_unlock_irqrestore(&task_data_events_lock, flags);

Is that lock taken in the context switch?

If not could be a normal spinlock, thus be more RT friendly.

-Andi