Re: [PATCH 2/9] perf: Allow pmu to choose cpu on which to installevent

[Anshuman Khandual]

On Wednesday 02 May 2012 07:37 AM, Yan, Zheng wrote:

> From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>
> 
> Allow the pmu->event_init callback to change event->cpu, so pmu can
> choose cpu on which to install event.
> 
> Signed-off-by: Zheng Yan <zheng.z.yan@xxxxxxxxx>
> ---
>  kernel/events/core.c |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 32cfc76..84911de 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6250,6 +6250,8 @@ SYSCALL_DEFINE5(perf_event_open,
>  		}
>  	}
> 
> +	get_online_cpus();

Why this protection against cpu hotplug operation ? Is this because PMU now can change event->cpu
during event initialization (specific to uncore PMU events) or this protection has always been required
for normal on-cpu HW PMU events also and we added it right now ?

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