linux-kernel - Re: [PATCH] perf_counter: extensible perf_counter

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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@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf_counter: extensible perf_counter_attr

Ingo Molnar writes:

> * Paul Mackerras <paulus@...ba.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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