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Message-ID: <20180522083920.GD31075@leoy-ThinkPad-X240s>
Date: Tue, 22 May 2018 16:39:20 +0800
From: Leo Yan <leo.yan@...aro.org>
To: Robert Walker <robert.walker@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Jonathan Corbet <corbet@....net>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.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-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, Tor Jeremiassen <tor@...com>,
mike.leach@...aro.org, kim.phillips@....com,
coresight@...ts.linaro.org, Mike Leach <mike.leach@....com>
Subject: Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets
Hi Rob,
On Mon, May 21, 2018 at 12:27:42PM +0100, Robert Walker wrote:
> Hi Leo,
>
> On 21/05/18 09:52, Leo Yan wrote:
> >Commit e573e978fb12 ("perf cs-etm: Inject capabilitity for CoreSight
> >traces") reworks the samples generation flow from CoreSight trace to
> >match the correct format so Perf report tool can display the samples
> >properly. But the change has side effect for packet handling, it only
> >generate samples when 'prev_packet->last_instr_taken_branch' is true,
> >this results in the start tracing packet and exception packets are
> >dropped.
> >
> >This patch checks extra two conditions for complete samples:
> >
> >- If 'prev_packet->sample_type' is zero we can use this condition to
> > get to know this is the start tracing packet; for this case, the start
> > packet's end_addr is zero as well so we need to handle it in the
> > function cs_etm__last_executed_instr();
> >
>
> I think you also need to add something in to handle discontinuities in
> trace - for example it is possible to configure the ETM to only trace
> execution in specific code regions or to trace a few cycles every so
> often. In these cases, prev_packet->sample_type will not be zero, but
> whatever the previous packet was. You will get a CS_ETM_TRACE_ON packet in
> such cases, generated by an I_TRACE_ON element in the trace stream.
> You also get this on exception return.
>
> However, you should also keep the test for prev_packet->sample_type == 0
> as you may not see a CS_ETM_TRACE_ON when decoding a buffer that has
> wrapped.
Thanks for reviewing. Let's dig more detailed into this issue,
especially for handling packet CS_ETM_TRACE_ON, I'd like divide into two
sub cases.
- The first case is for using python script:
I use python script to analyze packets with below command:
./perf script --itrace=ril128 -s arm-cs-trace-disasm.py -F cpu,event,ip,addr,sym -- -v -d objdump -k ./vmlinux
What I observe is after we pass python script with parameter '-s
arm-cs-trace-disasm.py', then instruction tracing options
'--itrace=ril128' isn't really used; the perf tool creates another
new process for launch python script and re-enter cmd_script()
function, but at the second time when invoke cmd_script() for python
script execution the option '--itrace=ril128' is dropped and all
parameters are only valid defined by the python script.
As result, I can the variable 'etmq->etm->synth_opts.last_branch' is
always FALSE for running python script. So all CS_ETM_TRACE_ON
packets will be ignored in the function cs_etm__flush().
Even the CS_ETM_TRACE_ON packets are missed to handle, the program
flow still can work well. The reason is without the interference by
CS_ETM_TRACE_ON, the CS_ETM_RANGE packets can smoothly create
instruction range by ignore the middle CS_ETM_TRACE_ON packet.
Please see below example, in this example there have 3 packets, the
first one packet is CS_ETM_RANGE packet which is labelled with
'PACKET_1', the first one packet can properly generate branch sample
data with previous packet as expected; the second packet is
PACKET_2 which is CS_ETM_TRACE_ON, but
'etmq->etm->synth_opts.last_branch' is false so function
cs_etm__flush() doesn't handle it and skip the swap operation
"etmq->prev_packet = tmp"; the third packet is PACKET_3, which is
CS_ETM_RANGE packet and we can see it's smoontly to create
continous instruction range between PACKET_1 and PACKET_3.
cs_etm__sample: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f79c end_addr=0xffff000008a5f7bc last_instr_taken_branch=1
PACKET_1: cs_etm__sample: packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1
cs_etm__synth_branch_sample: ip=0xffff000008a5f7b8 addr=0xffff000008a5f858 pid=2290 tid=2290 id=1000000021 stream_id=1000000021 period=1 cpu=1 flags=0 cpumode=2
cs_etm__flush: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1
PACKET_2: cs_etm__flush: packet: sample_type=2 exc=0 exc_ret=0 cpu=2 start_addr=0xdeadbeefdeadbeef end_addr=0xdeadbeefdeadbeef last_instr_taken_branch=1
cs_etm__sample: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1
PACKET_3: cs_etm__sample: packet: sample_type=1 exc=0 exc_ret=0 cpu=2 start_addr=0xffff000008be7528 end_addr=0xffff000008be7538 last_instr_taken_branch=1
cs_etm__synth_branch_sample: ip=0xffff000008a5f860 addr=0xffff000008be7528 pid=2290 tid=2290 id=1000000021 stream_id=1000000021 period=1 cpu=2 flags=0 cpumode=2
So seems to me, the CS_ETM_TRACE_ON packet doesn't introduce trouble
for the program flow analysis if we can handle all CS_ETM_RANGE
packets and without handling CS_ETM_TRACE_ON packet for branch
samples.
- The second case is for --itrace option without python script:
./perf script --itrace=ril -F cpu,event,ip,addr,sym -k ./vmlinux
In this case, the flag 'etmq->etm->synth_opts.last_branch' is true
so CS_ETM_TRACE_ON packet will be handled; but I can observe the
CS_ETM_RANGE packet in etmq->prev_packet isn't handled in the
function cs_etm__flush() for branch sample, so actually we miss some
branch sample for this case.
So I think we also need handle CS_ETM_RANGE packet in function
cs_etm__flush() to generate branch samples. But this has side
effect, we introduce the extra track for CS_ETM_TRACE_ON packet for
branch samples, so we will see one branch range like:
[ 0xdeadbeefdeadbeef .. 0xdeadbeefdeadbeef ].
Please reivew below change is okay for you? Thanks a lot for
suggestions.
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 822ba91..37d3722 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -495,6 +495,13 @@ static inline void cs_etm__reset_last_branch_rb(struct cs_etm_queue *etmq)
static inline u64 cs_etm__last_executed_instr(struct cs_etm_packet *packet)
{
/*
+ * The packet is the start tracing packet if the end_addr is zero,
+ * returns 0 for this case.
+ */
+ if (!packet->end_addr)
+ return 0;
+
+ /*
* The packet records the execution range with an exclusive end address
*
* A64 instructions are constant size, so the last executed
@@ -897,13 +904,28 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
etmq->period_instructions = instrs_over;
}
- if (etm->sample_branches &&
- etmq->prev_packet &&
- etmq->prev_packet->sample_type == CS_ETM_RANGE &&
- etmq->prev_packet->last_instr_taken_branch) {
- ret = cs_etm__synth_branch_sample(etmq);
- if (ret)
- return ret;
+ if (etm->sample_branches && etmq->prev_packet) {
+ bool generate_sample = false;
+
+ /* Generate sample for start tracing packet */
+ if (etmq->prev_packet->sample_type == 0 ||
+ etmq->prev_packet->sample_type == CS_ETM_TRACE_ON)
+ generate_sample = true;
+
+ /* Generate sample for exception packet */
+ if (etmq->prev_packet->exc == true)
+ generate_sample = true;
+
+ /* Generate sample for normal branch packet */
+ if (etmq->prev_packet->sample_type == CS_ETM_RANGE &&
+ etmq->prev_packet->last_instr_taken_branch)
+ generate_sample = true;
+
+ if (generate_sample) {
+ ret = cs_etm__synth_branch_sample(etmq);
+ if (ret)
+ return ret;
+ }
}
if (etm->sample_branches || etm->synth_opts.last_branch) {
@@ -921,12 +943,17 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
static int cs_etm__flush(struct cs_etm_queue *etmq)
{
+ struct cs_etm_auxtrace *etm = etmq->etm;
int err = 0;
struct cs_etm_packet *tmp;
- if (etmq->etm->synth_opts.last_branch &&
- etmq->prev_packet &&
- etmq->prev_packet->sample_type == CS_ETM_RANGE) {
+ if (!etmq->prev_packet)
+ return 0;
+
+ if (etmq->prev_packet->sample_type != CS_ETM_RANGE)
+ return 0;
+
+ if (etmq->etm->synth_opts.last_branch) {
/*
* Generate a last branch event for the branches left in the
* circular buffer at the end of the trace.
@@ -939,18 +966,25 @@ static int cs_etm__flush(struct cs_etm_queue *etmq)
err = cs_etm__synth_instruction_sample(
etmq, addr,
etmq->period_instructions);
+ if (err)
+ return err;
etmq->period_instructions = 0;
+ }
- /*
- * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
- * the next incoming packet.
- */
- tmp = etmq->packet;
- etmq->packet = etmq->prev_packet;
- etmq->prev_packet = tmp;
+ if (etm->sample_branches) {
+ err = cs_etm__synth_branch_sample(etmq);
+ if (err)
+ return err;
}
- return err;
+ /*
+ * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
+ * the next incoming packet.
+ */
+ tmp = etmq->packet;
+ etmq->packet = etmq->prev_packet;
+ etmq->prev_packet = tmp;
+ return 0;
}
static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
--
2.7.4
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