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Message-ID: <18990.12846.941708.201337@cargo.ozlabs.ibm.com>
Date: Tue, 9 Jun 2009 19:58:06 +1000
From: Paul Mackerras <paulus@samba.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>,
       Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
       Thomas Gleixner <tglx@linutronix.de>,
       Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] perf_counter: extensible perf_counter_attr
In-Reply-To: <20090609065350.GB16707@elte.hu>
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	<18989.57919.895309.847520@drongo.ozlabs.ibm.com>
	<20090609065350.GB16707@elte.hu>
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Ingo Molnar writes:

> * Paul Mackerras <paulus@samba.org> wrote:

> > Since this is a user-visible structure, you've just introduced an 
> > ABI difference between 32-bit and 64-bit processes, which we've 
> > managed to avoid so far. [...]
> 
> This is a good point too - handling pointers in ABIs is possible but 
> should be avoided as much as possible: it creates the need to 
> introduce a compat_sys_perf_counter_open() and doubles the syscall 
> table complexity.
> 
> Lets do the s/__reserved_1/attr_size ABI i suggested (i outlined 
> various properties of it in the previous mail). Agreed?

Yep, sounds good.

We also need a way to allow access to random machine-specific features
that might not be supported in a generic way, such as the instruction
matching CAM on POWER4/PPC970, or (apparently) PEBS.  That's what I
had intended exclusive groups + the extra_config_len field to be used
for, but Peter removed extra_config_len...

Paul.
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