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drmemtrace -trace_after_instrs introduces gap between first and second timestamps #6745

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abhinav92003 opened this issue Mar 29, 2024 · 1 comment · May be fixed by #6746
Open

drmemtrace -trace_after_instrs introduces gap between first and second timestamps #6745

abhinav92003 opened this issue Mar 29, 2024 · 1 comment · May be fixed by #6746
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@abhinav92003
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@abhinav92003
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When drmemtrace tracing is done with -trace_after_instrs enabled, the timestamp in the trace buffer at thread-init is set to the then timestamp, but trace entries start pouring in only after the specified count of instrs have passed. This introduces a gap in the first and second timestamp in the trace, which is directly proportional to the requested -trace_after_instrs value.

For a simple_app trace collected using:

$ ./bin64/drrun -t drcachesim -offline -trace_after_instrs 100000 -- suite/tests/bin/simple_app

grepping for timestamps in the view tool output shows the diff.

$ grep timestamp /tmp/view.txt 
           6           0:     1922821 <marker: timestamp 13356213906110890>
       12485        9005:     1922821 <marker: timestamp 13356213907576928> <--- much after the first timestamp
       12487        9005:     1922821 <marker: timestamp 13356213907577279>
       15494       11278:     1922821 <marker: timestamp 13356213907766531>
       15497       11278:     1922821 <marker: timestamp 13356213907766846>
       21119       15375:     1922821 <marker: timestamp 13356213907800740>
@abhinav92003 abhinav92003 self-assigned this Mar 29, 2024
abhinav92003 added a commit that referenced this issue Mar 29, 2024
@abhinav92003
i#6745: Fix timestamp gap in -trace_after_instrs
14e306a 
Fixes a timestamp gap between the first and second timestamps in the trace
caused when -trace_after_instrs is used.

Fixes: #6745
@abhinav92003 abhinav92003 linked a pull request Mar 29, 2024 that will close this issue
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@derekbruening
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Sounds like the timestamp solutions involving freezing or using restart timestamps for windows #6104 just need to include this delayed-trace case. Also xref the original frozen timestamps in #2039 and #5021.

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i#6745: Fix timestamp gap in delayed tracing DynamoRIO/dynamorio
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@abhinav92003 @derekbruening