openkylin
/
linux
mirror of https://gitee.com/openkylin/linux.git
9
0
Fork 0
Code Issues Projects Releases Wiki Activity

perf cs-etm: Correct synthesizing instruction samples 

When 'etm->instructions_sample_period' is less than
'tidq->period_instructions', the function cs_etm__sample() cannot handle
this case properly with its logic.

Let's see below flow as an example:

- If we set itrace option '--itrace=i4', then function cs_etm__sample()
  has variables with initialized values:

  tidq->period_instructions = 0
  etm->instructions_sample_period = 4

- When the first packet is coming:

  packet->instr_count = 10; the number of instructions executed in this
  packet is 10, thus update period_instructions as below:

  tidq->period_instructions = 0 + 10 = 10
  instrs_over = 10 - 4 = 6
  offset = 10 - 6 - 1 = 3
  tidq->period_instructions = instrs_over = 6

- When the second packet is coming:

  packet->instr_count = 10; in the second pass, assume 10 instructions
  in the trace sample again:

  tidq->period_instructions = 6 + 10 = 16
  instrs_over = 16 - 4 = 12
  offset = 10 - 12 - 1 = -3  -> the negative value
  tidq->period_instructions = instrs_over = 12

So after handle these two packets, there have below issues:

The first issue is that cs_etm__instr_addr() returns the address within
the current trace sample of the instruction related to offset, so the
offset is supposed to be always unsigned value.  But in fact, function
cs_etm__sample() might calculate a negative offset value (in handling
the second packet, the offset is -3) and pass to cs_etm__instr_addr()
with u64 type with a big positive integer.

The second issue is it only synthesizes 2 samples for sample period = 4.
In theory, every packet has 10 instructions so the two packets have
total 20 instructions, 20 instructions should generate 5 samples
(4 x 5 = 20).  This is because cs_etm__sample() only calls once
cs_etm__synth_instruction_sample() to generate instruction sample per
range packet.

This patch fixes the logic in function cs_etm__sample(); the basic
idea for handling coming packet is:

- To synthesize the first instruction sample, it combines the left
  instructions from the previous packet and the head of the new
  packet; then generate continuous samples with sample period;
- At the tail of the new packet, if it has the rest instructions,
  these instructions will be left for the sequential sample.

Suggested-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Walker <robert.walker@arm.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight ml <coresight@lists.linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lore.kernel.org/lkml/20200219021811.20067-4-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Leo Yan 2020-02-19 10:18:09 +08:00 committed by Arnaldo Carvalho de Melo
parent f1410028c7
commit c9f5baa136
1 changed files with 70 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

87
tools/perf/util/cs-etm.c
View File

@ -1358,9 +1358,12 @@ static int cs_etm__sample(struct cs_etm_queue *etmq,
struct cs_etm_auxtrace *etm = etmq->etm;
int ret;
u8 trace_chan_id = tidq->trace_chan_id;
u64 instrs_executed = tidq->packet->instr_count;
u64 instrs_prev;
tidq->period_instructions += instrs_executed;
/* Get instructions remainder from previous packet */
instrs_prev = tidq->period_instructions;
tidq->period_instructions += tidq->packet->instr_count;
/*
* Record a branch when the last instruction in
@ -1378,26 +1381,76 @@ static int cs_etm__sample(struct cs_etm_queue *etmq,
* TODO: allow period to be defined in cycles and clock time
*/
/* Get number of instructions executed after the sample point */
u64 instrs_over = tidq->period_instructions -
etm->instructions_sample_period;
/*
* Below diagram demonstrates the instruction samples
* generation flows:
*
* Instrs Instrs Instrs Instrs
* Sample(n) Sample(n+1) Sample(n+2) Sample(n+3)
* | | | |
* V V V V
* --------------------------------------------------
* ^ ^
* | |
* Period Period
* instructions(Pi) instructions(Pi')
*
* | |
* \---------------- -----------------/
* V
* tidq->packet->instr_count
*
* Instrs Sample(n...) are the synthesised samples occurring
* every etm->instructions_sample_period instructions - as
* defined on the perf command line. Sample(n) is being the
* last sample before the current etm packet, n+1 to n+3
* samples are generated from the current etm packet.
*
* tidq->packet->instr_count represents the number of
* instructions in the current etm packet.
*
* Period instructions (Pi) contains the the number of
* instructions executed after the sample point(n) from the
* previous etm packet. This will always be less than
* etm->instructions_sample_period.
*
* When generate new samples, it combines with two parts
* instructions, one is the tail of the old packet and another
* is the head of the new coming packet, to generate
* sample(n+1); sample(n+2) and sample(n+3) consume the
* instructions with sample period. After sample(n+3), the rest
* instructions will be used by later packet and it is assigned
* to tidq->period_instructions for next round calculation.
*/
/*
* Calculate the address of the sampled instruction (-1 as
* sample is reported as though instruction has just been
* executed, but PC has not advanced to next instruction)
* Get the initial offset into the current packet instructions;
* entry conditions ensure that instrs_prev is less than
* etm->instructions_sample_period.
*/
u64 offset = (instrs_executed - instrs_over - 1);
u64 addr = cs_etm__instr_addr(etmq, trace_chan_id,
tidq->packet, offset);
u64 offset = etm->instructions_sample_period - instrs_prev;
u64 addr;
ret = cs_etm__synth_instruction_sample(
etmq, tidq, addr, etm->instructions_sample_period);
if (ret)
return ret;
while (tidq->period_instructions >=
etm->instructions_sample_period) {
/*
* Calculate the address of the sampled instruction (-1
* as sample is reported as though instruction has just
* been executed, but PC has not advanced to next
* instruction)
*/
addr = cs_etm__instr_addr(etmq, trace_chan_id,
tidq->packet, offset - 1);
ret = cs_etm__synth_instruction_sample(
etmq, tidq, addr,
etm->instructions_sample_period);
if (ret)
return ret;
/* Carry remaining instructions into next sample period */
tidq->period_instructions = instrs_over;
offset += etm->instructions_sample_period;
tidq->period_instructions -=
etm->instructions_sample_period;
}
}
if (etm->sample_branches) {