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Subject: Re: Perf: Preserving the event across CPU hotunplug/plug and Creation
 of an event on offine CPU
From:   Mukesh Ojha <mojha@codeaurora.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
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Message-ID: <4f276f87-b6d8-f868-b3e7-9951d1383070@codeaurora.org>
Date:   Tue, 28 May 2019 21:46:42 +0530
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On 5/23/2019 6:39 PM, Mukesh Ojha wrote:
> Hi Peter/All,
>
> This is regarding the discussion happen in the past about 
> https://lkml.org/lkml/2018/2/15/1324
>
> Where the exact ask is to allow preserving and creation of events on a 
> offline CPU, so that when the CPU
> comes online it will start counting.
>
> I had a look at your patch too and resolve crash during while trying 
> to create an event on an offline cpu.
>
> In your patch,  you seem to disable event when cpu goes offline which 
> is exactly deleting the event
> from the pmu and add when it comes online, it seems to  work.
>
> But, For the purpose of allowing the creation of event while CPU is 
> offline is not able to count event while
> CPU coming online, for that i did some change, that did work.
>
> Also, I have query about the events which gets destroyed while CPU is 
> offline and we need to remove them
> once cpu comes online right ? As Raghavendra also queried the same in 
> the above thread.
>
> Don't we need  a list where we maintain the events which gets 
> destroyed while CPU is dead ?
> and clean it  up when CPU comes online ?
>
> Thanks.
> Mukesh
>
>