linux-kernel - Re: [PATCH] perf: Fix intel shared extra msr allocation

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Date:	Tue, 5 Jun 2012 12:21:21 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"Yan, Zheng" <zheng.z.yan@...ux.intel.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Fix intel shared extra msr allocation

On Tue, Jun 5, 2012 at 12:14 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Fri, 2012-06-01 at 22:11 +0800, Yan, Zheng wrote:
>>
>> The real problem is from __intel_shared_reg_put_constraints(). it set
>> reg->alloc to 0
>
> ok
>
>> and decreases fake_cpuc->shared_regs->regs[reg->idx]'s
>> reference count.
>
> So? That's fake state, who cares what its left in?
>
Right, that's what I am trying to elucidate. Who cares about it
beyond validate_group()? The fake_cpuc is reallocated for each
validate group. And this includes the fake shared_regs.

>> Later when deleting the event,  put_constraints() will find
>> reg->alloc is 0 and it won't decrease the shared msr's reference count.
>
> OK, so the only problem is us setting reg->alloc to 0?

I agree with the first part of the patch in intel_try_alt_er(), we
should not touch
the actual event struct. But I am still unclear about the reg->alloc part.
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