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In some situations 'perf script -F +brstackinsn' sees a lot of "not
reaching sample" messages.
This happens when the last LBR block before the sample contains a branch
that is not in the LBR, and the instruction dumping stops.
$ perf record -b emacs -Q --batch '()'
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.396 MB perf.data (443 samples) ]
$ perf script -F +brstackinsn
...
00007f0ab2d171a4 insn: 41 0f 94 c0
00007f0ab2d171a8 insn: 83 fa 01
00007f0ab2d171ab insn: 74 d3 # PRED 6 cycles [313] 1.00 IPC
00007f0ab2d17180 insn: 45 84 c0
00007f0ab2d17183 insn: 74 28
... not reaching sample ...
$ perf script -F +brstackinsn | grep -c reach
136
$
This is a problem for further analysis that wants to see the full code
upto the sample.
There are two common cases where the message is bogus:
- The LBR only logs taken branches, but the branch might be a
conditional branch that is not taken (that is the most common case
actually)
- The LBR sampling uses a filter ignoring some branches, but the perf
script check checks for all branches.
This patch fixes these two conditions, by only checking for conditional
branches, as well as checking the perf_event_attr's branch filter
attributes.
For the test case above it fixes all the messages:
$ ./perf script -F +brstackinsn | grep -c reach
0
Note that there are still conditions when the message is hit --
sometimes there can be a unconditional branch that misses the LBR update
before the sample -- but they are much more rare now.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20240229161828.386397-1-ak@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
24 lines
471 B
C
24 lines
471 B
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/compiler.h>
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#include "dump-insn.h"
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/* Fallback code */
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__weak
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const char *dump_insn(struct perf_insn *x __maybe_unused,
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u64 ip __maybe_unused, u8 *inbuf __maybe_unused,
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int inlen __maybe_unused, int *lenp)
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{
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if (lenp)
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*lenp = 0;
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return "?";
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}
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__weak
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int arch_is_uncond_branch(const unsigned char *buf __maybe_unused,
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size_t len __maybe_unused,
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int x86_64 __maybe_unused)
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{
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return 0;
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}
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