linux-kernel - Re: [PATCH 5/7] powerpc/perf: Define big-endian version of perf_mem_data

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Message-ID: <20130811171535.GA31780@us.ibm.com>
Date:	Sun, 11 Aug 2013 10:15:35 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Vince Weaver <vince@...ter.net>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Stephane Eranian <eranian@...gle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@....ibm.com>,
	Michael Ellerman <michael@...erman.id.au>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH 5/7] powerpc/perf: Define big-endian version of
 perf_mem_data_src

Vince Weaver [vince@...ter.net] wrote:
| On Sat, 10 Aug 2013, Sukadev Bhattiprolu wrote:
| 
| > 
| >  include/uapi/linux/perf_event.h |   55 +++++++++++++++++++++++++++++++++++++++
| >  1 files changed, 55 insertions(+), 0 deletions(-)
| 
| > +#define __PERF_LE	1234
| > +#define __PERF_BE	4321
| > +
| > +#if defined(__KERNEL__)
| 
| I could be wrong, but I thought files under uapi weren't supposed to 
| contain __KERNEL__ code.  Wasn't that the whole point of uapi?
| 
| Also having the perf_event interface depend on endianess just seems like a 
| complicated mess.  Can't we just declare the interface to be a certain 
| endianess and have the kernel byte-swap as necessary?

Except for the __KERNEL__ check, it looked like this approach would keep
the kernel and user code same. Would it complicate user space ?

I tried to avoid the __KERNEL__ check hack, but like I tried to explain
in the patch, user space and kernel do the endian check differently. 
And, there are about ~300 sites in the kernel with __*ENDIAN checks

Sukadev

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