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

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Date:	Wed, 24 Oct 2012 16:37:28 +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 04:23 PM, Yan, Zheng wrote:
> 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.
> 

Sorry, I mean patch 2.

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