linux-kernel - Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

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Date:	Tue, 23 Oct 2012 12:11:36 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, eranian@...gle.com,
	ak@...ux.intel.com
Subject: Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

On Tue, 2012-10-23 at 13:41 +0800, Yan, Zheng wrote:
> On 10/22/2012 06:35 PM, Peter Zijlstra wrote:
> > On Mon, 2012-10-22 at 14:11 +0800, Yan, Zheng wrote:
> >> --- a/include/uapi/linux/perf_event.h
> >> +++ b/include/uapi/linux/perf_event.h
> >> @@ -160,8 +160,9 @@ enum perf_branch_sample_type {
> >>         PERF_SAMPLE_BRANCH_ABORT        = 1U << 7, /* transaction aborts */
> >>         PERF_SAMPLE_BRANCH_INTX         = 1U << 8, /* in transaction (flag) */
> >>         PERF_SAMPLE_BRANCH_NOTX         = 1U << 9, /* not in transaction (flag) */
> >> +       PERF_SAMPLE_BRANCH_CALL_STACK   = 1U << 10, /* call stack */
> >>  
> >> -       PERF_SAMPLE_BRANCH_MAX          = 1U << 10, /* non-ABI */
> >> +       PERF_SAMPLE_BRANCH_MAX          = 1U << 11, /* non-ABI */
> >>  }; 
> > 
> > You add an ABI sample type without mentioning it in your changelog.. I
> > think I'll stop reading here.
> > 
> Ok, I will add the ABI change to the change log. Do you think we should hide this
> branch sample type from user?

Possibly not, I haven't really thought about it. But never hide an ABI
change. Explicitly mention it and preferably explain why you felt it
needed to extend the ABI.
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