Hi Tanmay,
On Thu, Mar 27, 2025 at 04:41:48PM +0530, Tanmay Jagdale wrote:
The existing method to synthesize instruction samples has the following issues:
- Branch instruction mnemonics were being added to non-branch instructions too.
- Branch target address was missing
To fix the issues, start synthesizing the instructions from the previous packet (tidq->prev_packet) instead of current packet (tidq->packet). This way it's easy to figure out the target address of the branch instruction in tidq->prev_packet which is the current packet's (tidq->packet) first executed instruction.
Since we have now switched to processing the previous packet first, we need not swap the packets during cs_etm__flush().
Signed-off-by: Tanmay Jagdale tanmay@marvell.com Reviewed-by: James Clark james.clark@arm.com
I saw James's reviewed tag. However, I have several comments.
Sorry I jumped in too late.
tools/perf/util/cs-etm.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c index 0bf9e5c27b59..ebed5b98860e 100644 --- a/tools/perf/util/cs-etm.c +++ b/tools/perf/util/cs-etm.c @@ -1576,10 +1576,26 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
Seems to me, the problem is cs_etm__synth_instruction_sample() is invoked from multiple callers.
Both the previous packet and packet are valid fo the flow: cs_etm__sample() `> cs_etm__synth_instruction_sample()
Only the previous packet is valid and the current packet stores stale data for the flows:
cs_etm__flush() `> cs_etm__synth_instruction_sample()
cs_etm__end_block() `> cs_etm__synth_instruction_sample()
First, as a prerequisite, I think we should resolve the stale data in the packet. So we need a fix like:
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c index 0bf9e5c27b59..b7b17c0e4806 100644 --- a/tools/perf/util/cs-etm.c +++ b/tools/perf/util/cs-etm.c @@ -741,6 +741,9 @@ static void cs_etm__packet_swap(struct cs_etm_auxtrace *etm,
if (etm->synth_opts.branches || etm->synth_opts.last_branch || etm->synth_opts.instructions) { + /* The previous packet will not be used, cleanup it */ + memset(tidq->prev_packet, 0x0, sizeof(*tidq->packet)); + /* * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for * the next incoming packet.
sample.stream_id = etmq->etm->instructions_id; sample.period = period; sample.cpu = tidq->packet->cpu;
Should we use "prev_packet->cpu" at here?
Even for a branch instruction, as its IP address is from the previous packet, we should use "prev_packet->cpu" for CPU ID as well.
- sample.flags = tidq->prev_packet->flags; sample.cpumode = event->sample.header.misc;
- cs_etm__copy_insn(etmq, tidq->trace_chan_id, tidq->packet, &sample);
- cs_etm__copy_insn(etmq, tidq->trace_chan_id, tidq->prev_packet, &sample);
- /* Populate branch target information only when we encounter
* branch instruction, which is at the end of tidq->prev_packet.*/- if (addr == (tidq->prev_packet->end_addr - 4)) {
if (!addr && addr == cs_etm__last_executed_instr(tidq->prev_packet))
/* Update the perf_sample flags using the prev_packet* since that is the queue we are synthesizing.*/sample.flags = tidq->prev_packet->flags;/* The last instruction of the previous queue would be a* branch operation. Get the target of that branch by looking* into the first executed instruction of the current packet* queue.*/sample.addr = cs_etm__first_executed_instr(tidq->packet);
If connected to the change suggested for cleaning up packet in cs_etm__packet_swap(), when run at here, if "tidq->packet" is a valid packet, then it will return a branch target address, otherwise, it will return 0.
- }
if (etm->synth_opts.last_branch) sample.branch_stack = tidq->last_branch; @@ -1771,7 +1787,7 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, /* Get instructions remainder from previous packet */ instrs_prev = tidq->period_instructions;
- tidq->period_instructions += tidq->packet->instr_count;
- tidq->period_instructions += tidq->prev_packet->instr_count;
A side effect for this change is we will defer to synthesize instruction samples for _current_ packet, either the packet will be handled after a new packet incoming, or at the end of a trace chunk.
The problem is for the later one, we can see cs_etm__end_block() and cs_etm__flush() both only handle the previous packet. As a result, the last packet will be ignored.
I would suggest we need to firstly fix this issue in cs_etm__end_block() and cs_etm__flush() (maybe we need to consider to consolidate the code with cs_etm__sample()).
/* * Record a branch when the last instruction in @@ -1851,8 +1867,11 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, * been executed, but PC has not advanced to next * instruction) */
/* Get address from prev_packet since we are synthesizing* that in cs_etm__synth_instruction_sample()*/ addr = cs_etm__instr_addr(etmq, trace_chan_id,
tidq->packet, offset - 1);
tidq->prev_packet, offset - 1); ret = cs_etm__synth_instruction_sample( etmq, tidq, addr, etm->instructions_sample_period);@@ -1916,7 +1935,7 @@ static int cs_etm__flush(struct cs_etm_queue *etmq, /* Handle start tracing packet */ if (tidq->prev_packet->sample_type == CS_ETM_EMPTY)
goto swap_packet;
goto reset_last_br;if (etmq->etm->synth_opts.last_branch && etmq->etm->synth_opts.instructions && @@ -1952,8 +1971,7 @@ static int cs_etm__flush(struct cs_etm_queue *etmq, return err; } -swap_packet:
- cs_etm__packet_swap(etm, tidq);
+reset_last_br:
As said, if we consolidate cs_etm__flush() for processing both previous packet and current packet, then we don't need to remove cs_etm__packet_swap() at here, right?
Thanks, Leo
/* Reset last branches after flush the trace */ if (etm->synth_opts.last_branch) -- 2.43.0