linux-kernel - Re: [PATCH v4 4/6] perf tools: enable dwarf_callchain

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Message-ID: <e7538b32-365e-7f0a-e77a-59d47febdd2e@arm.com>
Date:   Fri, 17 Dec 2021 12:08:59 +0000
From:   German Gomez <german.gomez@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org, Alexandre Truong <alexandre.truong@....com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 4/6] perf tools: enable dwarf_callchain_users on arm64


On 15/12/2021 16:37, Mark Rutland wrote:
> On Wed, Dec 15, 2021 at 03:11:36PM +0000, German Gomez wrote:
>> [...]
>>
>> +
>> +	/*
>> +	 * It's possible to determine the caller of leaf frames with omitted
>> +	 * frame pointers on aarch64 using libunwind, so enable it.
>> +	 */
> I reckon it's worth mentioning *why* we need to do this; how about:
>
> 	/*
> 	 * It's necessary to use libunwind to reliably determine the caller of
> 	 * a leaf function on aarch64, as otherwise we cannot know whether to
> 	 * start from the LR or FP.
> 	 *
> 	 * Always starting from the LR can result in duplicate or entirely
> 	 * erroneous entries. Always skipping the LR and starting from the FP
> 	 * can result in missing entries.
> 	 */
>
> Other than that, this looks fine to me!
>
> Thanks,
> Mark.


Ack, I will update this

Thanks,
German

>
>> +	if (callchain_param.record_mode == CALLCHAIN_FP && !strcmp(arch, "arm64"))
>> +		dwarf_callchain_users = true;
>>  }
>>  
>>  static bool chain_match(struct callchain_list *base_chain,
>> diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
>> index 77fba053c677..d95615daed73 100644
>> --- a/tools/perf/util/callchain.h
>> +++ b/tools/perf/util/callchain.h
>> @@ -300,7 +300,7 @@ int callchain_branch_counts(struct callchain_root *root,
>>  			    u64 *branch_count, u64 *predicted_count,
>>  			    u64 *abort_count, u64 *cycles_count);
>>  
>> -void callchain_param_setup(u64 sample_type);
>> +void callchain_param_setup(u64 sample_type, const char *arch);
>>  
>>  bool callchain_cnode_matched(struct callchain_node *base_cnode,
>>  			     struct callchain_node *pair_cnode);
>> -- 
>> 2.25.1
>>