linux-kernel - Re: [PATCH 01/10] perf/core, x86: Add PERF_SAMPLE_LBR

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Message-ID: <3ac026c3-6b9c-a6c1-2c2b-c7ecdbb22b1d@linux.intel.com>
Date:   Tue, 8 Oct 2019 09:53:24 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...nel.org, namhyung@...nel.org, ak@...ux.intel.com,
        vitaly.slobodskoy@...el.com, pavel.gerasimov@...el.com
Subject: Re: [PATCH 01/10] perf/core, x86: Add PERF_SAMPLE_LBR_TOS



On 10/8/2019 4:31 AM, Peter Zijlstra wrote:
> On Mon, Oct 07, 2019 at 10:59:01AM -0700, kan.liang@...ux.intel.com wrote:
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 61448c19a132..ee9ef0c4cb08 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -100,6 +100,7 @@ struct perf_raw_record {
>>    */
>>   struct perf_branch_stack {
>>   	__u64				nr;
>> +	__u64				tos;
>>   	struct perf_branch_entry	entries[0];
>>   };
>>   
>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>> index bb7b271397a6..fe36ebb7dc2e 100644
>> --- a/include/uapi/linux/perf_event.h
>> +++ b/include/uapi/linux/perf_event.h
>> @@ -141,8 +141,9 @@ enum perf_event_sample_format {
>>   	PERF_SAMPLE_TRANSACTION			= 1U << 17,
>>   	PERF_SAMPLE_REGS_INTR			= 1U << 18,
>>   	PERF_SAMPLE_PHYS_ADDR			= 1U << 19,
>> +	PERF_SAMPLE_LBR_TOS			= 1U << 20,
>>   
>> -	PERF_SAMPLE_MAX = 1U << 20,		/* non-ABI */
>> +	PERF_SAMPLE_MAX = 1U << 21,		/* non-ABI */
>>   
>>   	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
>>   };
>> @@ -864,6 +865,7 @@ enum perf_event_type {
>>   	 *	{ u64			abi; # enum perf_sample_regs_abi
>>   	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
>>   	 *	{ u64			phys_addr;} && PERF_SAMPLE_PHYS_ADDR
>> +	 *	{ u64			tos;} && PERF_SAMPLE_LBR_TOS
>>   	 * };
>>   	 */
>>   	PERF_RECORD_SAMPLE			= 9,
> 
> I have problems with the API.. You're introducing the intel specific LBR
> naming, and adding a whole new sample type vs extending the existing
> BRANCH_STACK (like you really already do with struct perf_branch_stack). >
> So why not add a bit to PERF_SAMPLE_BRANCH_* to request the presence of
> the TOS field in the PERF_SAMPLE_BRANCH_STACK output?

We never store PERF_SAMPLE_BRANCH_* in a sample. The perf tool cannot 
tell if the sample includes TOS field.
There will be a problem when a new perf tool parsing the data generated 
by an old kernel.


Can we rename the new sample type PERF_SAMPLE_BRANCH_STACK_EXTENSION?

{ u64			version;
   u64			tos;} 		&& PERF_SAMPLE_LBR_TOS

If other platforms want to add their extension, we just need to increase 
the version number. Perf tool will check the version before parsing the 
sample.

Thanks,
Kan