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Date: Mon, 3 Feb 2020 09:52:01 +0800
From: Leo Yan <leo.yan@...aro.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Suzuki K Poulose <suzuki.poulose@....com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Mike Leach <mike.leach@...aro.org>,
Robert Walker <robert.walker@....com>,
Coresight ML <coresight@...ts.linaro.org>
Cc: Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v3 3/5] 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 is to divide into three parts for handling coming packet:
- The first part is for synthesizing the first instruction sample, it
combines the instructions from the tail of previous packet and the
instructions from the head of the new packet;
- The second part is to simply generate samples with sample period
aligned;
- The third part is the tail of new packet, the rest instructions will
be left for the sequential sample handling.
Suggested-by: Mike Leach <mike.leach@...aro.org>
Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
tools/perf/util/cs-etm.c | 105 ++++++++++++++++++++++++++++++++++-----
1 file changed, 92 insertions(+), 13 deletions(-)
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 3e28462609e7..c5a05f728eac 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -1360,23 +1360,102 @@ 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
+ * instrs_executed
+ *
+ * Period instructions (Pi) contains the the number of
+ * instructions executed after the sample point(n). When a new
+ * instruction packet is coming and generate for the next sample
+ * (n+1), it combines with two parts instructions, one is the
+ * tail of the old packet and another is the head of the new
+ * coming packet. So 'head' variable is used to cauclate the
+ * instruction numbers in the new packet for sample(n+1).
+ *
+ * Sample(n+2) and sample(n+3) consume the instructions with
+ * sample period, so directly generate samples based on the
+ * sampe period.
+ *
+ * After sample(n+3), the rest instructions will be used by
+ * later packet; so use 'instrs_over' to track the rest
+ * instruction number and it is assigned to
+ * 'tidq->period_instructions' for next round calculation.
+ */
+ u64 head, offset = 0;
+ u64 addr;
/*
- * 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)
+ * 'instrs_over' is the number of instructions executed after
+ * sample points, initialise it to 'instrs_executed' and will
+ * decrease it for consumed instructions in every synthesized
+ * instruction sample.
*/
- u64 offset = (instrs_executed - instrs_over - 1);
- u64 addr = cs_etm__instr_addr(etmq, trace_chan_id,
- tidq->packet, offset);
+ u64 instrs_over = instrs_executed;
- ret = cs_etm__synth_instruction_sample(
- etmq, tidq, addr, etm->instructions_sample_period);
- if (ret)
- return ret;
+ /*
+ * 'head' is the instructions number of the head in the new
+ * packet, it combines with the tail of previous packet to
+ * generate a sample. So 'head' uses the sample period to
+ * decrease the instruction number introduced by the previous
+ * packet.
+ */
+ head = etm->instructions_sample_period -
+ (tidq->period_instructions - instrs_executed);
+
+ if (head) {
+ offset = head;
+
+ /*
+ * 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;
+
+ instrs_over -= head;
+ }
+
+ while (instrs_over >= etm->instructions_sample_period) {
+ offset += 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;
+
+ instrs_over -= etm->instructions_sample_period;
+ }
/* Carry remaining instructions into next sample period */
tidq->period_instructions = instrs_over;
--
2.17.1
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