linux-kernel - Re: [RFC PATCH] perfcounters: provide expansion room in the ABI

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Date:	Thu, 5 Mar 2009 09:46:05 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC PATCH] perfcounters: provide expansion room in the ABI

Ingo Molnar wrote:

> > git://git.kernel.org/pub/scm/linux/kernel/git/paulus/perfcounters.git rfc
> > 
> >  include/linux/perf_counter.h |   12 +++++++++---
> >  include/linux/syscalls.h     |    2 +-
> >  kernel/perf_counter.c        |   10 +++++++---
> >  3 files changed, 17 insertions(+), 7 deletions(-)
> 
> Pulled into tip:perfcounters/core, thanks Paul!

Actually, I goofed slightly.  In this bit of the patch:

@@ -80,10 +81,15 @@ struct perf_counter_hw_event {
 				exclude_user   :  1, /* don't count user      */
 				exclude_kernel :  1, /* ditto kernel          */
 				exclude_hv     :  1, /* ditto hypervisor      */
+				exclude_idle   :  1, /* don't count when idle */
 
-				__reserved_1 : 23;
+				__reserved_1 : 55;
+

the 55 should have been 54 if we want those bitfields to occupy 64
bits.  With 55 there, __reserved_1 will go in the next 64-bit
quadword (x86-speak, or doubleword in powerpc-speak).

Do you think that's worth changing?  If so I'll do a commit changing
the 55 to 54.

Paul.
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