linux-kernel - Re: [patch 05/24] perfmon: X86 generic code (x86)

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Message-ID: <7c86c4470811270547y370e0be6keef6aadffa16581f@mail.gmail.com>
Date:	Thu, 27 Nov 2008 14:47:20 +0100
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, x86@...nel.org, sfr@...b.auug.org.au
Subject: Re: [patch 05/24] perfmon: X86 generic code (x86)

On Thu, Nov 27, 2008 at 2:49 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> What about a thread doing this and another one in the middle of read the buffer?
>
> I assume that uses locks. Locking between threads is easy.
>
I think that is fine as long as the interrupt handler does not need to
grab locks.
But that, in turn, means that the state needed/modified by the handler cannot
be altered in any other way that could be harmful.

>>
>> Or what about a thread trying to reset the buffer while you're processing an PMU
>> interrupt on another CPU. I know each buffer is per-CPU, but that does not
>> prevent two threads for trying to operate on it at the same time from
>> different CPUs.
>
> That happens per CPU.
>
So you're saying a thread can only access the buffer from the CPU it
is running on?
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