Subject: Re: [PATCH v1 2/3] perf cs-etm: Add callchain to instruction sample

From: Mathieu Poirier <[email-masked]>
Date: Tue, 3 Sep 2019 16:07:23 -0600

On Fri, Aug 30, 2019 at 02:24:20PM +0800, Leo Yan wrote:
> Firstly, this patch adds support for the thread stack; when every branch
> packet is coming we will push or pop the stack based on the sample
> flags.
> 
> Secondly, based on the thread stack we can synthesize call chain for the
> instruction sample, this can be used by itrace option '--itrace=g'.
>

In most cases using the word "secondly" is a good indication the patch should be
split.
 
> Signed-off-by: Leo Yan <[email-masked]>
> ---
>  tools/perf/util/cs-etm.c | 74 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 73 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 882a0718033d..ad573d3bd305 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -17,6 +17,7 @@
>  #include <stdlib.h>
>  
>  #include "auxtrace.h"
> +#include "callchain.h"
>  #include "color.h"
>  #include "cs-etm.h"
>  #include "cs-etm-decoder/cs-etm-decoder.h"
> @@ -69,6 +70,7 @@ struct cs_etm_traceid_queue {
>  	size_t last_branch_pos;
>  	union perf_event *event_buf;
>  	struct thread *thread;
> +	struct ip_callchain *chain;
>  	struct branch_stack *last_branch;
>  	struct branch_stack *last_branch_rb;
>  	struct cs_etm_packet *prev_packet;
> @@ -246,6 +248,16 @@ static int cs_etm__init_traceid_queue(struct cs_etm_queue *etmq,
>  	if (!tidq->prev_packet)
>  		goto out_free;
>  
> +	if (etm->synth_opts.callchain) {
> +		size_t sz = sizeof(struct ip_callchain);
> +
> +		/* Add 1 to callchain_sz for callchain context */
> +		sz += (etm->synth_opts.callchain_sz + 1) * sizeof(u64);
> +		tidq->chain = zalloc(sz);
> +		if (!tidq->chain)
> +			goto out_free;
> +	}
> +
>  	if (etm->synth_opts.last_branch) {
>  		size_t sz = sizeof(struct branch_stack);
>  
> @@ -270,6 +282,7 @@ static int cs_etm__init_traceid_queue(struct cs_etm_queue *etmq,
>  	zfree(&tidq->last_branch);
>  	zfree(&tidq->prev_packet);
>  	zfree(&tidq->packet);
> +	zfree(&tidq->chain);
>  out:
>  	return rc;
>  }
> @@ -541,6 +554,7 @@ static void cs_etm__free_traceid_queues(struct cs_etm_queue *etmq)
>  		zfree(&tidq->last_branch_rb);
>  		zfree(&tidq->prev_packet);
>  		zfree(&tidq->packet);
> +		zfree(&tidq->chain);
>  		zfree(&tidq);
>  
>  		/*
> @@ -1121,6 +1135,41 @@ static void cs_etm__copy_insn(struct cs_etm_queue *etmq,
>  			   sample->insn_len, (void *)sample->insn);
>  }
>  
> +static void cs_etm__add_stack_event(struct cs_etm_queue *etmq,
> +				    struct cs_etm_traceid_queue *tidq)
> +{
> +	struct cs_etm_auxtrace *etm = etmq->etm;
> +	u8 trace_chan_id = tidq->trace_chan_id;
> +	int insn_len;
> +	u64 from_ip, to_ip;
> +
> +	if (etm->synth_opts.callchain || etm->synth_opts.thread_stack) {
> +
> +		from_ip = cs_etm__last_executed_instr(tidq->prev_packet);
> +		to_ip = cs_etm__first_executed_instr(tidq->packet);
> +
> +		/*
> +		 * T32 instruction size might be 32-bit or 16-bit, decide by
> +		 * calling cs_etm__t32_instr_size().
> +		 */
> +		if (tidq->prev_packet->isa == CS_ETM_ISA_T32)
> +			insn_len = cs_etm__t32_instr_size(etmq, trace_chan_id,
> +							  from_ip);
> +		/* Otherwise, A64 and A32 instruction size are always 32-bit. */
> +		else
> +			insn_len = 4;
> +
> +		thread_stack__event(tidq->thread, tidq->prev_packet->cpu,
> +				    tidq->prev_packet->flags,
> +				    from_ip, to_ip, insn_len,
> +				    etmq->buffer->buffer_nr);
> +	} else {
> +		thread_stack__set_trace_nr(tidq->thread,
> +					   tidq->prev_packet->cpu,
> +					   etmq->buffer->buffer_nr);

Please add a comment on what the above does.  As a rule of thumb I add a comment
per addition in a patch in order to help people understand what is happening and
some of the reasonning behing the code.

> +	}
> +}
> +
>  static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
>  					    struct cs_etm_traceid_queue *tidq,
>  					    u64 addr, u64 period)
> @@ -1146,6 +1195,14 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
>  
>  	cs_etm__copy_insn(etmq, tidq->trace_chan_id, tidq->packet, &sample);
>  
> +	if (etm->synth_opts.callchain) {
> +		thread_stack__sample(tidq->thread, tidq->packet->cpu,
> +				     tidq->chain,
> +				     etm->synth_opts.callchain_sz + 1,
> +				     sample.ip, etm->kernel_start);
> +		sample.callchain = tidq->chain;
> +	}
> +
>  	if (etm->synth_opts.last_branch) {
>  		cs_etm__copy_last_branch_rb(etmq, tidq);
>  		sample.branch_stack = tidq->last_branch;
> @@ -1329,6 +1386,8 @@ static int cs_etm__synth_events(struct cs_etm_auxtrace *etm,
>  		attr.sample_type &= ~(u64)PERF_SAMPLE_ADDR;
>  	}
>  
> +	if (etm->synth_opts.callchain)
> +		attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
>  	if (etm->synth_opts.last_branch)
>  		attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
>  
> @@ -1397,6 +1456,9 @@ static int cs_etm__sample(struct cs_etm_queue *etmq,
>  		tidq->period_instructions = instrs_over;
>  	}
>  
> +	if (tidq->prev_packet->last_instr_taken_branch)
> +		cs_etm__add_stack_event(etmq, tidq);
> +
>  	if (etm->sample_branches) {
>  		bool generate_sample = false;
>  
> @@ -2596,7 +2658,17 @@ int cs_etm__process_auxtrace_info(union perf_event *event,
>  	} else {
>  		itrace_synth_opts__set_default(&etm->synth_opts,
>  				session->itrace_synth_opts->default_no_sample);
> -		etm->synth_opts.callchain = false;
> +
> +		etm->synth_opts.thread_stack =
> +				session->itrace_synth_opts->thread_stack;
> +	}
> +
> +	if (etm->synth_opts.callchain && !symbol_conf.use_callchain) {
> +		symbol_conf.use_callchain = true;
> +		if (callchain_register_param(&callchain_param) < 0) {
> +			symbol_conf.use_callchain = false;
> +			etm->synth_opts.callchain = false;
> +		}
>  	}
>  
>  	err = cs_etm__synth_events(etm, session);
> -- 
> 2.17.1
> 

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