Subject: Re: [PATCH V4 09/10] power8, perf: Change BHRB branch filter configuration

From: Anshuman Khandual <[email-masked]>
Date: Wed, 18 Dec 2013 09:25:36 +0530

On 12/18/2013 05:38 AM, Michael Ellerman wrote:
> On Fri, 2013-12-13 at 13:50 +0530, Anshuman Khandual wrote:
>> On 12/09/2013 11:51 AM, Michael Ellerman wrote:
>>>
>>> As I said in my comments on version 3 which you ignored:
>>>
>>>     I think it would be clearer if we actually checked for the possibilities we
>>>     allow and let everything else fall through, eg:
>>>
>>> Â Â Â Â Â Â Â Â /* Ignore user/kernel/hv bits */
>>> Â Â Â Â Â Â Â Â branch_sample_type &= ~PERF_SAMPLE_BRANCH_PLM_ALL;
>>>
>>> Â Â Â Â Â Â Â Â if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY)
>>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â return 0;
>>>
>>> Â Â Â Â Â Â Â Â if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY_CALL)
>>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â return POWER8_MMCRA_IFM1;
>>> Â 
>>> Â Â Â Â Â Â Â Â if (branch_sample_type == PERF_SAMPLE_BRANCH_COND)
>>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â return POWER8_MMCRA_IFM3;
>>> Â Â Â Â Â Â Â Â 
>>> Â Â Â Â Â Â Â Â return -1;
>>>
>>
>> Hey Michael,
>>
>> This patch only adds support for the PERF_SAMPLE_BRANCH_COND filter, if the
>> over all code flow does not clearly suggest that all combinations of any of
>> these HW filters are invalid, then we can go with one more patch to clean
>> that up before or after this patch but not here in this patch. Finally the
>> code section here will look something like this. Does it sound good ?
> 
> Better, but not quite.
> 
>> static u64 power8_bhrb_filter_map(u64 branch_sample_type)
>> {
>>         u64 pmu_bhrb_filter = 0;
>>
>>         /* BHRB and regular PMU events share the same privilege state
>>          * filter configuration. BHRB is always recorded along with a
>>          * regular PMU event. As the privilege state filter is handled
>>          * in the basic PMC configuration of the accompanying regular
>>          * PMU event, we ignore any separate BHRB specific request.
>>          */
>>
>>         /* Ignore user, kernel, hv bits */
>>         branch_sample_type &= ~PERF_SAMPLE_BRANCH_PLM_ALL;
>>
>>         if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY)
>>                 return pmu_bhrb_filter;
> 
> return 0;
> 
>>
>>
>>         if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY_CALL) {
>>                 pmu_bhrb_filter |= POWER8_MMCRA_IFM1;
>>                 return pmu_bhrb_filter;
> 
> return POWER8_MMCRA_IFM1;
> 
>>         }
>>
>>         if (branch_sample_type == PERF_SAMPLE_BRANCH_COND) {
>>                 pmu_bhrb_filter |= POWER8_MMCRA_IFM3;
>>                 return pmu_bhrb_filter;
> 
> return POWER8_MMCRA_IFM3;
> 
>>         }
>>
>>         /* Every thing else is unsupported */
>>         return -1;
>> }
> 

Okay, will take these changes into another patch before adding conditional branch
filter here.