linux-kernel - Re: [PATCH V2 1/7] perf, x86: Reduce lbr_sel

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Message-ID: <5087A574.3040507@intel.com>
Date:	Wed, 24 Oct 2012 16:23:16 +0800
From:	"Yan, Zheng" <zheng.z.yan@...el.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH V2 1/7] perf, x86: Reduce lbr_sel_map size

On 10/24/2012 04:15 PM, Stephane Eranian wrote:
> On Wed, Oct 24, 2012 at 9:49 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
>> On 10/24/2012 03:28 PM, Stephane Eranian wrote:
>>> On Wed, Oct 24, 2012 at 7:59 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
>>>> From: "Yan, Zheng" <zheng.z.yan@...el.com>
>>>>
>>>> The index of lbr_sel_map is bit value of perf branch_sample_type.
>>>> By using bit shift as index, we can reduce lbr_sel_map size.
>>>>
>>>> Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
>>>> ---
>>>>  arch/x86/kernel/cpu/perf_event.h           |  4 +++
>>>>  arch/x86/kernel/cpu/perf_event_intel_lbr.c | 50 ++++++++++++++----------------
>>>>  include/uapi/linux/perf_event.h            | 42 +++++++++++++++++--------
>>>>  3 files changed, 56 insertions(+), 40 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
>>>> index d3b3bb7..ea6749a 100644
>>>> --- a/arch/x86/kernel/cpu/perf_event.h
>>>> +++ b/arch/x86/kernel/cpu/perf_event.h
>>>> @@ -412,6 +412,10 @@ struct x86_pmu {
>>>>         struct perf_guest_switch_msr *(*guest_get_msrs)(int *nr);
>>>>  };
>>>>
>>>> +enum {
>>>> +       PERF_SAMPLE_BRANCH_SELECT_MAP_SIZE = PERF_SAMPLE_BRANCH_MAX_SHIFT,
>>>> +};
>>>> +
>>> What's the point on the extraneous definition?
>>
>> because later patches will add map PERF_SAMPLE_BRANCH_CALL_STACK, it will make
>> "PERF_SAMPLE_BRANCH_SELECT_MAP_SIZE != PERF_SAMPLE_BRANCH_MAX_SHIFT"
>>
> And you are not going to do:
> 
> enum perf_branch_sample_type_shift {
> ...
> PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT = 10
> PERF_SAMPLE_BRANCH_MAX_SHIFT
> };
> 
> PERF_SAMPLE_BRANCH_CALL_STACK = 1 << PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT
> 
> Unless you're telling you are not going to add a mapping for
> PERF_SAMPLE_CALL_STACK to the
> lbr_sel_map[]?
> 

I think include/uapi/linux/perf_event.h should only contain definition for user API.
So I added PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT and PERF_SAMPLE_BRANCH_CALL_STACK to
arch/x86/kernel/cpu/perf_event.h. Please check patch 1.

Regards
Yan, Zheng

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