perf intel-pt: Fix instructions sampling rate

commit 7ba8fa20e26eb3c0c04d747f7fd2223694eac4d5 upstream.

The timestamp used to determine if an instruction sample is made, is an
estimate based on the number of instructions since the last known
timestamp. A consequence is that it might go backwards, which results in
extra samples. Change it so that a sample is only made when the
timestamp goes forwards.

Note this does not affect a sampling period of 0 or sampling periods
specified as a count of instructions.

Example:

 Before:

 $ perf script --itrace=i10us
 ls 13812 [003] 2167315.222583:       3270 instructions:u:      7fac71e2e494 __GI___tunables_init+0xf4 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:      30902 instructions:u:      7fac71e2da0f _dl_cache_libcmp+0x2f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         10 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          8 instructions:u:      7fac71e2d9ea _dl_cache_libcmp+0xa (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         14 instructions:u:      7fac71e2d9ea _dl_cache_libcmp+0xa (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          6 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:         14 instructions:u:      7fac71e2d9ff _dl_cache_libcmp+0x1f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:          4 instructions:u:      7fac71e2dab2 _dl_cache_libcmp+0xd2 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222728:      16423 instructions:u:      7fac71e2477a _dl_map_object_deps+0x1ba (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222734:      12731 instructions:u:      7fac71e27938 _dl_name_match_p+0x68 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ...

 After:
 $ perf script --itrace=i10us
 ls 13812 [003] 2167315.222583:       3270 instructions:u:      7fac71e2e494 __GI___tunables_init+0xf4 (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222667:      30902 instructions:u:      7fac71e2da0f _dl_cache_libcmp+0x2f (/lib/x86_64-linux-gnu/ld-2.28.so)
 ls 13812 [003] 2167315.222728:      16479 instructions:u:      7fac71e2477a _dl_map_object_deps+0x1ba (/lib/x86_64-linux-gnu/ld-2.28.so)
 ...

Signed-off-by: Adrian Hunter <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: [email protected]
Fixes: f4aa081 ("perf tools: Add Intel PT decoder")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

tools/perf/util/intel-pt-decoder/intel-pt-decoder.c

@@ -888,16 +888,20 @@ static uint64_t intel_pt_next_period(struct intel_pt_decoder *decoder)
 	timestamp = decoder->timestamp + decoder->timestamp_insn_cnt;
 	masked_timestamp = timestamp & decoder->period_mask;
 	if (decoder->continuous_period) {
-		if (masked_timestamp != decoder->last_masked_timestamp)
+		if (masked_timestamp > decoder->last_masked_timestamp)
 			return 1;
 	} else {
 		timestamp += 1;
 		masked_timestamp = timestamp & decoder->period_mask;
-		if (masked_timestamp != decoder->last_masked_timestamp) {
+		if (masked_timestamp > decoder->last_masked_timestamp) {
 			decoder->last_masked_timestamp = masked_timestamp;
 			decoder->continuous_period = true;
 		}
 	}
+
+	if (masked_timestamp < decoder->last_masked_timestamp)
+		return decoder->period_ticks;
+
 	return decoder->period_ticks - (timestamp - masked_timestamp);
 }
 
@@ -926,7 +930,10 @@ static void intel_pt_sample_insn(struct intel_pt_decoder *decoder)
 	case INTEL_PT_PERIOD_TICKS:
 		timestamp = decoder->timestamp + decoder->timestamp_insn_cnt;
 		masked_timestamp = timestamp & decoder->period_mask;
-		decoder->last_masked_timestamp = masked_timestamp;
+		if (masked_timestamp > decoder->last_masked_timestamp)
+			decoder->last_masked_timestamp = masked_timestamp;
+		else
+			decoder->last_masked_timestamp += decoder->period_ticks;
 		break;
 	case INTEL_PT_PERIOD_NONE:
 	case INTEL_PT_PERIOD_MTC: